[Lonman]

It's not necessarily a matter of blowing people out of the bar it's properly matching the amp to the speakers program rating for maximum efficiency & clarity - and less chance of possible blowing the speakers. If a speakers program rating is 500 watts, then that's what your amp should push. Yes it will make sound & even seem loud with a lower powered amp, but it's also increasing the possibility of driving the amp into clipping if the extra volume is needed plus it isn't going to be able to really push a nice full clean signal throughout the frequency range. More power will make regluar listening levels seem fuller & seemingly louder because of it meaning the system doesn't need to be turned up as loud to achieve the same effect.
The Acesonic is actually not a 300 watt per channel @ 8 ohms amp, they list that as the specs, but if you look it's actually a peak rating. The 4 ohms per channel RMS (continuous) rating is 200 watts per channel meaning the 8 ohm continuous rating is probably closer to 125-150 watts per channel.