volume control of green bullet

hi there,

maybe a complete newbie-question... 

the shure green bullet mic has a volume contol as you all know I guess. until now i mostly use this to prevend feedback when listening to the recording i made without muting the channel.... while recording I always got the volume to 90 - 100 %.... so now my question: when is it suitable to play with middle volume settings? what's the advantage of adjusting the mic to 50% instead of using the gain of the amp or my usb-inteface while recording? would be great to get to know how mic, interface or amp adjustment are depending on each other...****think

greetings  - kai