No blitz is just as bad as lots of blitz, you have to do it in a moderate amount--Robert0905.
Blitz & Bullet is bad for your chess

I'd say that too much blitz is definitely not too good for you. But (whether this is true or not) I view blitz as a chess variant, which helps me to separate the games in my mind. Time is a tangible element in blitz, which means I use a different strategy. It's the same with any other variant I play. Making this distinction helps me to not see marked decline in my normal chess playing. Of course, I'm not very good at blitz anyway! :P

From several very advanced players I have heard from, some 5-minute games can actually be beneficial (even for an advanced beginner). For example, I was told they can be useful to run through openings.

I think that too much can be bad especially at the wrong time like just before a tournament. It does not seem to have hurt Nakamura. Anatoly Karpov says they do it. It is a ritual. Kramnik said to limit it though he did not say how strict the limit should be. Bobby Fischer did it regardless of what he said. It is good if it is not overdone. For most of us knowing when to stop may be the real problem. lol
Blitz chess kills your ideas. - Bobby Fischer
I play way too much blitz chess. It rots the brain just as surely as alcohol. - Nigel Short
Like dogs who sniff each other when meeting, chess players have a ritual at first acquaintance: they sit down to play speed chess. - Anatoly Karpov
In blitz, the knight is stronger than the bishop. - Vlastmil Hort
Playing rapid chess, one can lose the habit of concentrating for several hours in serious chess. That is why, if a player has big aims, he should limit his rapidplay in favour of serious chess. - Vladimir Kramnik
Yes, I have played a blitz game once. It was on a train, in 1929. - Mikhail Botvinnik
He who analyses blitz is stupid. - Rashid Nezhmetdinov
It is very difficult to play a single blitz game! You want to play for a long time. So I tend not to do that anymore. - Viswanathan Anand