Lot to cover here, I'll go by caliber.
All .32 brass because nobody else shoots it and those who do do not leave it at the range.
All revolver brass is worth keeping because even tho .38 and .357 are still popular and brass is relatively easy to get free, it lasts so long there's no reason not to keep it. .41, .44, and .45 Colt are all rare to find at the range, so don't throw any of that away.
As to semi auto, 9mm is useless to keep because you can scoop that stuff up by the bucket full at literally any shooting range. .380... I really don't know anyone who reloads that, but it's not as impossible to get as it use to be, however people do not shoot it in large amounts because the small guns aren't fun to shoot more than 50 rounds at a time.
10mm you must never let go of, it's popularity is increasing, but it's not there yet. I found near 200 cases of it at my range weeks ago and thought I hit the jackpot. Never seen any brass in 10 before, probably never will again. Which lead me to .40 in that if you already have 10mm and load for that, you don't need to bother keeping your .40 brass unless you really like shooting a .40.
.45 ACP is about the same category as 9mm, gonna be on the ground at every range you go to, no real need to keep any brass.
The one I can't touch on is bottleneck stuff like 5.7x38 and .357 Sig. I've read that 5.7 brass is basically toast after the first firing it stretches so much, .357 Sig IDK. I would just as easily tell people not to bother with either, the only bottleneck pistol I think is worth loading for is .32 NAA, but the guns and die sets are rare to find.