This. This. No biggie - it's actually pretty simple, but if nobody teaches you you'd never know. You wear it snug enough that when you breathe into your BELLY and flex your core muscles hard they press out against the belt, greatly increasing the amount of force they can put out vs just bracing your core against the air. If you crank it down too tight though, you won't have room to optimally flex (or breathe) and you will be relying on the belt to pretty much act AS your core support instead of bolstering it. Better than nothing, but the best power & support comes from bracing against the belt. Think about how much force you can exert just pressing your arm out, then how much you can exert if you're pressing against a surface like a wall. Same principle. This might not be desirable if part of the purpose is to try to restrict the waiste though, like DD mentioned. I know a lot of serious builders here who live and breathe by that dogma.