I have recently purchased new heads for my drums, but I'm reluctant to put them on now because the old heads still sound fine even though some of the coating is wearing off and getting dark in the center. There are no dents in the heads, so why change them? It seems like a waste of perfectly good heads.
Like guitar strings, a head that's broken-in is in its prime, and as long as it sounds good, there's really no reason to replace it. But after repeated tensioning, it will lose elasticity and no longer vibrates well, and it then needs to be replaced (unless you happen to like a dead, choked sound.)
I prefer worked in heads too, but don't like large pata-ches of missing coating. I always kind of admired the beat up heads I see on pics and clips of old blues, jazz, and Motown drummers. They clearly liked the sound too, or at least didn't feel the need to replace them that often.