Nothing much. Without monitors, you have to play by feeling... Basist and a guitarist can hear themselves on amplifiers (of course) and if you play with acoustic drums, that is heard... Played a while in the band where a drumer had electric drums... And we played in a restaurant, or whatever it was. Restaurant, I think. So we had to play quiet... And the speakers were in front of us. At the start, bummer. Didn"t have monitors at the time... But, after a while, you get kind of used to it. Just, everyone has to be reeeealy exact. Know what I mean? And it goes. But, playing with monitors feels like heaven afterwards... :)