Is powerfull Amps only for low sensitivity speakes?

This may be interesting: http://www.harbeth.co.uk/usergroup/forum/the-science-of-audio/amplifier-matching-mismatching-and-cli...
The point is that with significant dynamic range the peak power required is much higher than the average. In the quoted example, if you need 1 watt on average, you will need 160 watt to cope with a 22 dB peak above that average.

@willemj 
Just crunched the numbers on that. My 30 watt amp is EASILY capable of delivering those kinds of impulses into a 4 ohm load to produce nearly 107dB. So.... What's the need for 500 watts? 

So I guess you started the equation with a lower power requirement for average level, by e.g. using more efficient speakers and/or a small listening room. And 4 Ohm is also pretty low.

+1 - Agree with Trelja and Noromance

From my 35+ years experience in this hobby, power corrupts, and have your ever really heard how loud 1 watt/channel can get?  We only have 1 set of ears and I like mine to last as long as possible.  A lesson I was taught many years ago by a stereo shop owner who was tone deaf but built the most amazing sounding speakers.

@willemj 
I based those numbers on what I'm sitting here dealing with in my condo. 90dB/V/M speakers about 12 feet away with usual boundary and coupling factors. I picked 4 ohm instead of the nominal 8 ohm rating Focal claims just for fun and it probably is more realistic. The F5 transitions out of class A into 4 ohm at 31 watts and easily carries the 24.5V and 6.1 amp to make for 150 watt transients. Looking around here, 12 feet seems a fairly average distance and 90dB sensitivity is pretty average sensitivity.