I usually just keep a couple of pieces. I've got a pair of stretch brown jeans that i have had for a really long time now. I don't need to wear them much even when i'm fat but i keep them because i really don't want to have to buy that sort of thing and they are useful in some situations. So i keep them.
I keep things i like but chuck out everything else. But not all at once. I wait for maybe one year and then chuck things out if they have been in storage too long.
I also keep skinny clothes in storage. They don't get a lot of use either. Fashions change.