How does everyone declutter? My Pokémon storage is full again

After the next event, my bag space is always instantly maxed out. I wanted to ask what everyone's usual criteria for cleaning out their bag are? Personally, I basically transfer any Pokémon that isn't IV 90+, a shiny, or a purified Pokémon. However, I feel reluctant to delete those with legacy moves or event-exclusive hat variants. Do you guys keep paying to expand your bag space, or do you strictly declutter? I'm really curious about everyone's storage management.