I keep an svg file of a straight line. Occasionally when I have mis-measured, done calculations wrong, etc - I just need just a cat hair taken off something. Ok ok, sometimes it is a bit more than a cat hair. Anyway, I just load my handy dandy line, resize it, move it to where I want it, and make the quick cut.
I have not seen anyone else mention this - if they have my apologies for re-stating your idea. This simple trick has saved me a bunch of times when I was too lazy to re-do a project but just needed a nudge to get one out of my MewPew.