I have SKS fenders on my Atlantis, and they're good and there's no reason to take them off in summer, but I do (we almost never get summer rain here). My beater is an old Trek tourer I converted to singlespeed, and it has fenders year round because it's what I ride in rain and snow.
No fenders on the mountain bike because mud gobs under them. But to be honest, I don't ride that much in mud anymore.