I think I’m in the minority here, but I don’t keep mine. I enjoy them when I get them, pass on a few to my fiancee and to my daughter if they’d be particularly interested in them, and with the rest, the stamps are cut off and sent to other PCers who collect stamps, then the cards go into the recycling.
Before anyone gets offended, I come from a childhood with a mom who was a hoarder and have struggled all my life with those tendencies as well. I’ve never gotten to the level it was with her, but I’m still trying to break away from that for myself and keeping anything ‘nonessential’ is a very bad idea for me. It rapidly turns into clutter which gets overwhelming.