Depends on the use - I throw them out (foam) if I go to the beach (sand, salt, etc- but use them more than one day if I'm on vacation for a few days at the beach), but dry them out & use again if only to the pool (chlorine seems to help deodorize/sanitize 'em)
I wear foam cushions til they 'disintegrate', but gels seem to last 'forever'.