Walking away from something and letting it "marinade" is a learning technique known as incubation .
When conscious, incubation occurs in the sub-conscious mind where your brain will continue to essentially run series of diagnostic tests addressing the problem it has been presented with.
When sleeping, incubation occurs in the unconscious mind, and some people might even have a dream about the problem they are dealing with.
This has been shown in mice wherein a given mouse was presented with a complicated maze.
When sleeping, electrodes attached to the mouse's brain illustrated the mouse running through the maze over and over, assimilated learned information.
The next day, the mouse was able to make it through the maze with little problem.
Incubation also has the added benefit allowing the person to approach the problem with a fresh perspective.
Typically, extended breaks from an instrument are not encouraged as a musician could lose a lot of fine motor-control and stamina.
That said, extended breaks can be beneficial.
For example, they could give a musician ample time to forget their bad playing / practice habits as well as renewing their enthusiasm and vigor for playing.
Small breaks (a few hours) are good and should be done often when practicing.
Long, extended breaks (a week or more) should not be done frequently at all and in fact used sparingly.
N.B. Mentally practicing is also quite beneficial.
If taking a break from your instrument, taking a practice session to mentally rehearse your music can aide in your practice as well.
music.stackexchange.com/users/3518/jjmusicnotes
Could be several things.
Certainly it takes time for repetitive practice elements to become part of "muscle memory," the name given to motions which no longer require the conscious portion of the brain to process.
Sometimes we just get sick of a song, or phrase, or technique, and need to take a deep breath (lasting days :-) )
and let our attitude reset itself.
I am a little skeptical that you can walk away for more than a week and be able to play with the speed, accuracy, and endurance you had before.
Certainly no professional-level musician would consider that possible; they generally find missing even a few days can affect their feeling of comfort/capability.
Granted for us hackers with a day job (:-) )
it's not as critical.
music.stackexchange.com/users/6275/Carl Witthoft
It can depend on a variety of things.
Often times, people don't practice as best they could, and actually end up wearing themselves out while trying to learn something.
If you wear yourself out everyday, without giving yourself time to rest, you will play a certain way.
After a while, it will be "normal" for you to play in this strained state.
So you may feel like you're playing better because when you take time off, you're giving your muscles time to heal.
It also depends on your playing level.
Obsession at a young-professional level can become a problem, and you may feel like you're playing better after a break, because you've forgotten all the little things you were obsessing about to your own detriment.
A lot of professionals do regularly take a week or two off from their instrument, to fully recharge.
It can be a very taxing activity on your muscles, depending on what instrument you play.
music.stackexchange.com/users/8848/elburzs
When improvising a solo or just messing about on guitar, I too find that I'm better at it and more imaginative when I've left the guitar alone for a while, perhaps a few days/a week.
The dexterity will be slightly diminished but I find that my choice of what to play is more inspired.
There's an optimum amount of time to break though - too short and theres no difference, too long and the connection with the instrumend diminishes.
I think best for me is about 4 days, but that's probably a personal thing.
I think what's happening is the 'rut' of familiar runs and riffs work their way from muscle memory back into my 'brain memory'
(ie, my set of ideas for that moment) and becomes "it's just what I do", until I break that habit and allow myself to forget it for a while.
Then I'm more open to a whole new set of riffs etc, and generally what feels to me like more interesting stuff.
music.stackexchange.com/users/7337/user2808054
I searched out this topic to see if it is indeed a labeled phenomenon.
I don't necessarily walk away from the instrument, but from some new, difficult pieces.
When I come back to them a week or two later, several of my previous "sticking" places in the music have miraculously worked themselves out.
I honestly believe it has something to do with hearing how it should be played in our head rather than hearing the "raw" version.
So perhaps our brains adjust the "raw" version into how it is supposed to sound while we sleep.
I don't know, but it is a little freaky!
Great, but freaky at the same time!
music.stackexchange.com/users/23007/Gruvergirl
I have noticed this too.
It's true for other things as well such as playing video games.
I think that when you take a break from something and come back later, your brain doesn't over-analyze as much as it did before.
When you're practicing something extensively, the brain is faced with many memories of things that worked and those that didn't.
During this time, there would be constant switching between these various little changes, which results in average performance.
But if you take a break and come back, your brain doesn't remember the little failures and will only work with what if knows works.
Another things that I noticed is that after I night of drinking alcohol, I notice that I perform better at tasks like music and video games.
This effect lasts for 2 days, and it decays completely by the third day.
Probably this is related as well.
music.stackexchange.com/users/8896/Hex4869
This is a thing.
It’s happened to me a few times now.
Just small breaks, 3-4 days, and I pick up and play things I never could before.
I never remember if I have had a dream but it makes sense to me that I might subconsciously rerun the things I have learnt and it becomes muscle memory without me realizing.
music.stackexchange.com/users/60881/Cordy
Sometimes as a musician, I find myself in a rut. My solution is to simply put my instrument down and walk away from it for a few weeks, sometimes even a month, and when I come back I'm better than when I was practicing every day.  I have my theories, that it gives my brain a chance to subconsciously process what I'd been learning, but I have nothing more than a guess.  Why does taking an extended break sometimes help?
Why does taking an extended break sometimes help?
music.stackexchange.com
<learning><practice>
music.stackexchange.com/questions/14365
music.stackexchange.com/users/8855/Dan Gayle
There may be many reasons why taking an extended break helps a musician. Obsession at a young-professional level can become a problem, and you may feel like you're playing better after a break, because you've forgotten all the little things you were obsessing about to your own detriment.  Often times, people don't practice as best they could, and actually end up wearing themselves out while trying to learn something. When you take a break from something and come back later, your brain doesn't over-analyze as much as it did before. This could depend on a variety of factors but the real answer is unclear. By taking a break, it's possible that you will be less inclined to over-analyse your performance and therefore your perception of your own performance will improve. Similarly, practising a lot will wear you out, so you are likely to be fresher after a break. Another possible reason is that a break will give you a chance to mentally rehearse the piece rather than just physically.
This could depend on a variety of factors. Taking a break from practice can help you to mentally rehearse what you were practising. Sometimes, over practising can mean that you simply wear yourself out. By taking a break, it's possible that you stop over-analysing things and your perception of your performance improves.