I use a sub for all my big gigs, almost every night & day......each room is different...
its up to your experience as a musician to determine what will sound best using your gear....there is no certain recipe, take sound checks,position speakers, make EQ adjustments all night long & most times during each song too to suit the room is the only way to get it right, and even then you might have to entertain on a wing & a prayer. Be ready for anything, be aware of what it sounds like out in the audience, and give em' 100% every time!!!

good luck