Collecting memes in your camera roll probably serves the same instinct that stamp collecting used to
that said if any FOSS devs want to make an app for categorizing and tagging memes outside the camera roll so i can use it for its intended purpose i will volunteer a (consensual) kiss on the forehead
I save them in my camera roll so that I can share them with people. I then just never delete them and they get lost. It is nice every once in a while to spot that random meme from 5 years ago and have a small chuckle.