It's a volume knob, LOL!!!
Seriously, these discussions about the all importance of preamps just make me giggle most of the time...especially when I hear peoples' bad music.
Do preamps matter? Answer: They Might. If you have the joy of capturing a great singer through the right mic in a decent room (or isolated) with a killer sound bed and cheap presonus preamps, guess what? It'll still sound great.
Am I completely blowing off the importance of a nice pre front? No; gain staging absolutely matters...it's just that for the vast majority of folks hanging around these boards (self included), the other 98% of the recording process (songwriting, performance, gear, mixing) is where the focus should be. If you want to spend assloads of money getting that last 2%, then you are entitled to do that...but don't do it until you've mastered the other 98% first. I honestly think that boutique preamps are where a lot of home recordists start to look for the "magic pixie dust" that their recordings are missing.
It's a volume knob. Keep it in perspective.