[Kronopath]

While the initial reason may be historical, I've found that on smaller monitors 80 character width makes it just about wide enough to have two code windows side-by-side. That's why I usually tend to stick to that limit. Though on bigger monitors I often stick to 100.

[mrweasel]

80 or 100 is both fine, but I prefer 80. Shorter lines are simply easier to read.

It just like reading a text online. Most people would prefer shorter lines, compared to one extremely long one. It's simply easier to keep track of where you are.

[pyotrgalois]

I usually use 100 or 120. It is very useful for having many windows on emacs on a 1920x1080 monitor. Also it is good for github. Anything bigger would need to scroll horizontally for reading the code and that sucks

[throwaway5752]

I always thought that it was because you might need to read or edit a file on a dumb terminal while troubleshooting a problematic system (eg, from single user mode or a rescue disk)

[Shivetya]

If I am on 3270 or 5250 I have 80/132 but for the most part even when using the PC based editors we have I find no issues with 80 columns because even on the wide screen monitor I have information panels and such taking up space, plus I can easily side by side code.

I am also of the opinion that like names, when the line gets too long the readability goes out the door