If you run 2560x1440 at its native resolution you can fit (4) side by side code windows at 80 characters with a very readable font size. Having 120 character lines only lets you have 2 (3 will cut off the last one by a decent amount).

Being able to comfortably open 4 files side by side is like having access to a completely new world compared to 2. You can often fit the entire context of what you're working on in one visible space.

I use 80 characters for mainly this reason and it's also no extra time spent when using languages like Python because Black will auto-format it for you, it comes down to running 1 command and letting the machine do all of the work.