An advantage is that you can conserve water because of less evaporation -- there's no sunshine.
A major disadvantage is the flip side: the sunshine can't help dry out plant leaves that get wet.
Some plants don't like cold and wet foliage.
These conditions can foster blight on tomatoes for example.
See also this answer that mentions being careful not to leave basil damp overnight.
So if you're watering in the evening, don't spray the foliage.
Use a soaker hose or other irrigation technique that targets the roots instead of the foliage.
Early morning is a good time to water.
You can give the soil a good soaking and everything has a chance to penetrate before being burned off by the sun.
Anything that gets on the foliage will dry up with the sun and you're less prone to disease and fungi.
gardening.stackexchange.com/users/51/bstpierre
If anything, the opposite is true.
There are two reasons: First is evaporation.
During the day it is hot and the water evaporates quickly - i.e. it is effectively wasted.
This is why cities and water authorities have recommendations, regulations, and by-laws controlling when you can use landscape irrigation systems.
Secondly, water on plants in the sun can cause scorching - regardless of your latitude.
This is because the water droplets act like small lenses, concentrating the sun.
So you really want the water to be off the plants when the sun is out.
This usually makes the evening at sunset (or after) more favorable to early morning watering.
Of course drip irrigation is another way of avoiding this problem.
gardening.stackexchange.com/users/69/winwaed
It is true that watering when the sun is out can cause scorching; on the other hand, although evening watering reduces evaporation, it leaves plants and the surrounding soil wet, or at least damp, at nightfall; besides providing fertile ground for diseases, this attracts more pests, particularly * slugs .
*
gardening.stackexchange.com/users/136/Mancuniensis
This link favours watering in the morning and, if that's not possible, then late afternoon (with enough time for the plant to dry out a little).
The dangers associated with scorching (daytime watering), are far outweighed by the problems associated with damp sulky plants (nighttime watering).
gardening.stackexchange.com/users/99/Tea Drinker
Here in the American South, in the summer, it's actually better to water plants in the evening, so that the water has a chance to soak in before it evaporates.
gardening.stackexchange.com/users/137/baka
It is only better to water in the evening or early morning from a conservation perspective due to evaporation of this precious resource.
Otherwise, the idea it's bad to be watered under the bright midday sun because it hurts the plants themselves appears to be a myth.
See this article by a well qualified horticulturist debunk it.
There are many causes of leaf scorch, but irrigation with fresh water is certainly not one of them.
Hundreds of scientific publications on crop plants, turf, woody shrubs and trees have examined foliar scorch, and not one of them has implicated midday irrigation as a causal agent.
What does cause damage, however, is suboptimal plant-water relations, which can result in tip and marginal leaf scorch, shoot dieback, stunted growth, and leaf abscission.
gardening.stackexchange.com/users/397/Lisa
Indeed, the best time to irrigate is in the morning and in the late afternoon for moisture to be absorbed by the plant with minimal evapotranspiration.
gardening.stackexchange.com/users/23952/Enock Mthreheya
Is it bad to water plants after the sun has gone down or near dusk?  If so, why?
Is it bad to water plants in the evening?
gardening.stackexchange.com
<watering><vegetables>
gardening.stackexchange.com/questions/545
gardening.stackexchange.com/users/178/Jim Geurts
You can conserve water as there is less evaporation so this is better during very hot weather. However, you do risk attracting slugs. Evening watering reduces evaporation, but leaves plants and the surrounding soil wet at nightfall; which can encourage disease and pests, particularly slugs . An additional advantge is that you conserve water due to less evaporation. Early morning is a good time to water and if not possible, then late afternoon. 
The dangers associated with scorching with daytime watering are far outweighed by the problems associated with evening watering.
Evening watering reduces evaporation, but leaves plants and the surrounding soil wet at nightfall; which can encourage disease and pests, particularly slugs . An additional advantge is that you conserve water due to less evaporation. Early morning is a good time to water and if not possible, then late afternoon. The dangers associated with scorching with daytime watering are far outweighed by the problems associated with evening watering.