How important are the first 3 rounds of a game?

I know they're important for setting the tone and economy, but i'm wondering how important they actually are in the grand scheme of things

No one care about first three we know half will end off with 9-3 / 8-4
And Other team will 50% probability will win

in lower lobbies setting tone yes since lose pistol=people quit

lose bonus = someone votes ff at 5th round