Why is 8.b4 bad ?

I often play this in blitz games

Both B4 and BE3 have been played at high levels on move 8.

Why do u think it is bad?

It is not bad at all.

Well the computer says it's bad and not seen played at the top level, much. I just play to gain space in blitz

"not seen played at the top leve"

Nobody (almost) at top level plays Nc3 anyway...

Or if they play it, they continue with either Na4 at some moment to win bishop pair, or Bg5-Bxf6-Nd5.

But some strong players played b4 here...

I wonder what is your engine, my Stockfish tells b4 is as good as many other moves, like Be3, Nd5, Bd2, h3...

It is a logical move, taking some space, giving a2 square for your bishop, i dont see why it would be a bad move.

At the bottom level

Thanks guys fot the replies :)

De nada.