We'll start with i design amps - and have done some in hgih end commercially.
Your question is a little bit vague, os let me re-pose it two ways:
1. Is the primary benefit of powerful amps the ability to drive inefficient or power hungry (big room, big capability) speakers? Yes.
2. Is there any *disadvantage* to powerful amps with efficient or small speakers? No.
There is nothing about a powerful amp that is inherently a compromise of sound for power except for one thing: the cost of a big transformer, many transistors, and heat-sinks necessary for big power. So in that sense there *is* a trade off; yet in those many-$1000 power amps, no such trade off has been made.
I have built my primary design in two formats: low power class-A (almost) and high power class A/AB, using nearly the same parts. They sound very similar, until one runs out of power and either clips or compresses. But that usually happens after my ears or the speakers are in distress.
Let's look at the flip side: modest power on large full-range speakers. I currently drive huge, 89 dB efficiency speakers (Mahlers if you care, very fussy) with the 60 wpc version with no problem. Most would select a higher power amp. I see no need, even though 3-4 are lying there idling, free for my use
So, within reason, select simply the best sounding amp. Also remember that there is more to "power" than rater power into an 8-ohm resistive load. Most speakers are FAR from an 8-ohm resistive load, and it may take some serious muscle to control them. That means low output impedance and ability to drive high current into a load that might drop to 2-ohms., or in many cases (read this carefully: negative impedance for a brief moment when the voice coil is traveling backwards). Electro magnets work both ways :-) And speakers are electro-magnets at their core.
Funny, on my moprning run, before reading your note, i was thinking about the best price/performance way to build a great, low cost (ok, maybe < $1000, so not that low), low power amp.
Happy listening.
G
