well, there may be more to it that you'd think.
And definitely an interesting piece of trivia.
There are 2 types of nibs, either as something sticking out like on the picture in the question, or as a little notch.
There are multiple answers, ranging from: nothing
, that's just for decoration
this can be used to attach a blade guard (so you tie the strings around it and it won't slip)
you can use it as a pivot point against a nail to draw a circle
(you lock your pencil in between 2 teeth).
woodworking.stackexchange.com/users/100/Pascal Belloncle
The explanation I'd always seen was that this "single tooth" could be used to create an initial nick in the wood to start the cut at a fairly precise place.
Without that nick, the first cut has a tendency to slip sideways a bit, losing accuracy.
You could create the guide nick in other ways -- with a chisel, for example -- perhaps more accurately.
But building it into the saw guarantees you'll have it when you need it.
I can't prove that was the original intent.
But I can say that it seems to work when used that way.
It's more a carpentry solution than a cabinetry solution, though, since it risks a bit more tear-out.
woodworking.stackexchange.com/users/91/keshlam
A trollish question indeed ;)
My favorite answer has been, "So you can recognize an old saw at garage sales," but the most well referenced sources I've found indicate that it was originally placed as a decoration and just stuck.
woodworking.stackexchange.com/users/180/Daniel B.
I wondered this for years
and so I emailed Christopher Schwarz (former editor of Popular Woodworking magazine and now owner of Lost Art Press .
He seems to research historical things very well and he responded that neither he nor anyone else knows for sure.
He said he had asked Roy Underhill (host of PBS's Woodwright's Shop) and a few others.
So, nobody knows for sure.
woodworking.stackexchange.com/users/178/glw
I always liked this answer
Some have said early handsaws had an auxiliary handle near the toe to guide the flexible saws and prevent them from bending.
The nib is said by them to be a vestigial handle which had become ornamental. from the Disstonian Institute
woodworking.stackexchange.com/users/29/Zach
Saw nibs have been present for hundreds of years. What is their purpose?
What is the purpose of a saw nib?
woodworking.stackexchange.com
<hand-tools><hand-saw>
woodworking.stackexchange.com/questions/539
woodworking.stackexchange.com/users/81/saltface
The explanation of a saw nib is a "single tooth" that could be used to create an initial nick in the wood to start the cut at a fairly precise place. Some say this  "single tooth" could be used to create an initial nick in the wood to start the cut at a fairly precise place. Others believe that early handsaws had an auxiliary handle near the toe to guide the flexible saws and prevent them from bending. The nib is sometimes said to be a vestigial handle which had become ornamental.
This "single tooth" could be used to create an initial nick in the wood to start the cut at a fairly precise place. Early handsaws had an auxiliary handle near the toe to guide the flexible saws and prevent them from bending. The nib is said to be a vestigial handle which had become ornamental.