Watts! How many do we need?

I have an original Schitt Aegir (20 w/ch 8 ohms) and a pair of Ohm 1000 speakers in a 15' X 24' room with a vaulted ceiling -- absolutely no problem reaching my desired listening level (85 dB average) with no hint of clipping or compressed dynamics.  Two caveats, however.  First I use a powered subwoofer and roll off the deep bass to the Ohms. Deep bass can be a power hog  Second, as many know, the relationship between watts and volume level is logarithmic, not linear. Doubling the power gets you 3 dB more volume. Doubling the perceived volume takes 10 times more power. So, if you are a headbanger, and have medium or low sensitive speakers, or have a large room, you're going to need a lot more power than I do.

But, as others have noted, lotsa watts are an attractive advertising carrot. And Class D amps have made it easier to offer that carrot these days.

@bigtwin -- the one thing missing in the info you posted is a reference to the listening volume in the room. Not everyone wants live rock concert volume in their home.

The other common mistake concerns the level of peaks above the average playback volume. People often think that recordings have more dramatic peaks than they actually do.  Digital recordings in particular have a max level that can't be exceeded. I've used Adobe Audition for years to edit all manner of recordings -- rock, folk, jazz, classical and others.  One thing I've noticed, in particular in reference to albums recorded since the advent of digital in studios, is the volume uniformity of drum strikes -- a common source of audible peaks in music. Viewed digitally, one can easily see that dynamic peaks have been limited during the recording process. The uniformity is is sharp contract to the variable peaks one sees from old LPs recorded on analog tape. Even with the latter there was a max possible volume that could recorded on the tape so limiters were still used so the average playback level wouldn't be too soft. No one wants the average level so low that background noise gets in the way.

@bigtwin -- I appreciate your points, but high wattage alone doesn't tell you anything about how an amp behaves when presented with a low impedance load of 4 ohms or under.  And wattage also says nothing about the other elements of sound quality. 

Especially since I don't listen at high levels (85 dB tops) I happen to enjoy my 20 w/ch (8 ohms) Aegir more than the 150 w/ch VTV amp I had immediately prior.

To use a car analogy, it is like focusing only on horsepower while ignoring torque, gearing, suspension, handling, braking and so on. (Of course, the same as with audio buffs, there are some car enthusiasts that will focus only on one trait.)