Keep them? Throw them away? Forget them until accidentally finding them years later? Burn them ritually? Shred them to dispose of the evidence? Or just never have any charts to begin with?
Not charted but do have a notebook full of notes for the 100+ songs learned in 30 days for the current band. Got an email in 2006 "Can you learn 100 songs in a month? We fired our bassist with an important gig coming up". Keep 'em in a file cabinet. Having to relearn or chart something years later, again, might be not fun.
I keep old charts in a file folder in case the same song(s) are needed in the future, but 9 times out of 10, I can never find that needed song in the pile. Jaco's Law of Charts: If you throw them away, you'll need them in the near future. If you keep them, you'll never need them.
I put them in sheet protectors inside a 3 ring binder. I really should scan them and save 'em as PDFs. Always come in handy for future projects.
if you're sure the bridge is burned but good, burn the "charts" & everything else to do with that band
If you quit on good terms - like you're having a kid, just time to go, etc and still friends, give them to the new bassist. It will help him/her immensely. If it was on less than great terms and it's not a lot of originals, keep them for future bands.
I recently threw all my paper song charts out and just keep everything on the tablet and use Mobile Sheets to access them. Also backed up to the computer. They do an 8 hour gig?? Surely they could have given you 3-4 sets worth to start.
One time this songwriter I auditioned for once freaked because he'd given me a few charts. It was his first time back out after writing songs for 2 years in his bedroom while he had a kid, and was convinced the whole world was waiting to rip off his genius songs. He made me mail them back to him. (No one wants your genius songs, I could always have photocopied them, must I really bother to cross the street and mail this for you, ack so much stupid). Other than that if it's a standard or a tune I like I keep it. Otherwise recycle.
I put everything on my ipad. It's good to have on hand. Only things I've ever deleted were stupid xmas tunes I had to do with one band that kept doing freebie charity gigs. When that band split, I deleted those charts so I have an excuse to never play rudolph the red nosed reindeer again.