If you are trying to hold an audience's attention (which you should be if you're playing in a pub, the landlord doesn't want his customers to get bored and walk off) you want to vary the pace, texture and tonality. If there are 8 players round the table and only 2 of them can do a tune in B flat, so much the better - a spot with fewer players making an entirely different sound will get the punters to stop, listen and maybe buy another round.

Scottish music uses an unusually wide variety of rhythms, keys and tempi, though not many sessions exploit all of it. (I often play much slower than anyone else in the session, and I can generate a spell of attentive silence when half an hour of high-speed jigs and reels have been all but lost in babble).