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?
Good chess players who play online prefer quick games like 10sec + 1 or 1 min because nobody can cheat with a computer engine for such short games.

If a player tries to cheat with a computer, in this type of game, he loses the game on time.

After many quick games, these players can maintain this balance easily. Indeed, they train brain to think very quickly. And those who can think quickly can think slowly. Thus, there is no problem playing slow games after fast games.

Moreover, just for your information, blitz game refers to all chess games where each player has up to 10 minutes for all the moves.