Blitz games can be helpful and can be damaging too, it depends on how you use it.
The problem with playing too much blitz is that your brain is getting used to play very fast which can be catastrophical in otb as the opponent would take his full time to make a move while you play it fast without thinking much of it.
In other hand, blitz is usefull for warming up your brain in the morning or to try openings and traps.
I have been playing alot of Blitz and i noticed my game has gotten worse in otb. Does Blitz damage your game? I noticed most IM's and GM's stay away from blitz before a tournament. I am trying to slow down my game so i can play tournaments in the USCF this year . Should i stop playing blitz?