How to choose a DJ or PA amplifier

How much power do I need?
Amplifier specifications are complicated.   Max power, peak power, rms power, impedance ratings like 8 ohms, ect...  The best advise I can give you after 40 years of experience as a band member and DJ is....  Get as much power as you can afford.  But won't too much power blow my speakers?  Usually not.  Usually too little power blows speakers.  Why?  Lets say you have 100 watt speakers and your amp is 100 watts.  Sounds like a perfect match, right?  Its not.  The 100 watt amp will have to play full blast all the time, just to get the speakers up to their full potential.  This causes the amp to get hot and put out distortion or to "clip".  Clipping is distortion.  And distortion kills speakers.  If you had a 300 watt amp, you could easily drive the speakers up to 100 watts using clean power with no distortion.  The amplifier will stay cool and cruise all night playing the speakers and you will achieve a clean clear sound.  Yes, you could turn the amp up all the way and damage the speakers.  But your ears probably won't let you.  The loud "popping sound" coming from your speakers would not be listenable and you would want to turn it down quick.  Where as clipping is hard to hear.  But don't be fooled, clipping will damage your speakers faster than popping them with too much power would.
I thought it was important to dispel the myth that matching power ratings with speakers and amps is the right thing to do, when really, its not.  Getting a large, powerful amplifier, is more important than which speakers to buy because it can power any speakers.