If, as you say, clashes are inevitable, is it a major problem? Who loses out, the promoters, the punters or both? Given a choice of two nighters, most punters are going to opt for the one they prefer, or if they like both, they'll probably go for the one that is closer to home. From a promoters point of view, if you find your event clashes with someone else's, then you may have to try a little harder to attract the punters. If you're a punter, then you may be spoilt for choice, which surely can't be a bad thing?