[quote name='51m0n' timestamp='1345233803' post='1775466']
Yeah there is, you wont be able to hear yourself against a drummer, and your tone will be a pile of doodoo due to having no headroom for the bass end
[/quote]
It is subject to the venue & other factors though. I've gigged with a 30w 1x12 combo in a 4 piece rock band & been able to hear myself (& be heard by the audience). Was not in a noisy pub/club venue though, but the drummer was a rather heavy hitter.
I've also gigged with 90w & 150w heads going into 1 or 2 1x15s in larger pub club venues & had no probs being heard. It's how much air you're moving, not how many watts you've got.