I typically pick up what I shoot plus what's in the stall that I use at our local range.
So I don't pick up a ton of other people's. But some gets in.
I shoot 9mm, 45 and 223/556 so I keep those.
I don't shoot 40 S&W but hold on to that too as one of my employees and a friend shoot it, so I may give it to them if they want to start reloading. If not I'll hang on to it as I could see a 40 coming home with me one day (but no time soon)
I also keep 308 as I can see that as a caliber I'll own one day.
Likewise, my mom has been talking about getting her carry permit so I hold onto the little bit of 380 that gets in with my brass.
I've also picked up some 300 Blackout so it'll join the 308 and 380 for possible future use.
Now the most interesting brass I've picked up is 38 special. I'm not sure how popular it is, but it's not a caliber I have any desire to shoot. So I posted here and a fellow forum member nearby took it. I figure getting it to someone who can use it was more important than trading as I have a bunch of brass in the calibers i shoot.
I'm hoping good karma will be shared as he said it was for his wife. So who know. Worse case, I got it to someone who will use it, best case I get some good luck!
So my suggestion is keep what you think you'll use, trade if you need something, and there's something nice about helping someone else so do it when you can.