I have a button on my amp that says "boost". when i have it turned on, i don't have to turn the gain/volume as high.

is that the main purpose behind the button, or is there a deeper explanation?

and does anyone else have a button on their amp like this.

oh and my amp is a 19 watt amp just so everyone knows.
i was just wondering because when i play i only have to put my gain on like 2, yet i get a pretty heavy crunch.