Why do titled players always play online (blitz) speed chess?

If you have been to an online chess server, you will notice that almost all titled players always play quick games (3 0) at a max.

On the other hand, if you go to tournaments, it needs cool thinking and not instantaneous moves.

I am surprised, then how do they maintain this balance? Doesn't playing too many quick games spoil their overall playing ability?

Doesn't hurt mine. I can switch from blitz to long games without problems. The reverse isn't true though... if I play a long game and then try blitz, I almost always end up thinking too long and either lose on time or due to time trouble.