It's interesting that no one has yet discussed the downsides to powerful amplifiers, as they are significant.
If a person is running an inefficient speaker (let's say 85 db. or less) or one that requires significant current due to low impedances in the bass or steep phase angles, then an amp with really stiff power supplies will, all else being equal, control the woofers better. When I write "amp with really stiff power supplies", however, I do not mean one that simply has a high wattage rating - as correctly noted above by several other posters, the fact that an amp has a high wattage rating does not necessarily mean that it has first-rate energy storage, e.g., Audio Research's 600 watt/channel monoblocks have less energy storage than CAT's 100 watt/channel JL-1 monoblocks.
Putting the issue of energy storage aside, there are two major disadvantages to high-powered amplifiers. First, it is very difficult to control a high-powered circuit without global feedback and virtually every high-powered amplifier therefore uses it. Global feedback sucks the life out of music by destroying three-dimensionality and giving it a closed-in, deadened quality, and can create highly complex distortion products. Most triode tube amps do not use global feedback, and well-known solid-state amps that do not use it include the darTZeel (Herve Deletraz HATES feedback), the Ayre monoblocks (Charlie Hanson HATES feedback), the new Rowland 625, a variety of Pass amps, and speaking of Sim, the Sim Audio W-5. Pass has made some very high-powered amps that do not use negative feedback, but most amps that eschew feedback are lower powered (the darTZeel and Sim put out roughly 150 watts/channel into 8 Ohms - the Ayre monos and the Rowland put out 300 watts/channel). For technical papers about negative feedback, see the Pass and Atma-Sphere websites.
The other downside of powerful amps is that they feature many output devices (by "output device", I mean output transistors in the case of solid-state amps and output tubes in the case of tube amps). All of those devices muck up the sound in systems that are otherwise high resolution because, among other reasons, it is very difficult to match output device pairs, every device adds noise, and they make the circuit more complex. For this reason, it is often said that the best sounding amp in an amp line is the lowest powered one. Most high-powered amps use a dozen or more output device pairs, while the darTZeel, in contrast, uses a single pair of transistors per channel. Circuit simplicity is indeed highly desirable - it's why many serious audiophiles put up with 8 watt (or less) per channel single-ended amps that use only one output device per channel.
If a person runs inefficient speakers in a large room and listens to electronic music (anything amplified and then recorded, like rock or pop), then high-wattage, brute force amps are arguably desirable. But if a person has reasonably efficient speakers (87+ db.), a normal-sized room, and listens mostly to unamplified acoustic instruments (classical, jazz), a high-powered amp will, relatively speaking, sound less like real instruments and more like an electronic reproduction.
So, how much difference does a more powerful amp make? It can make a huge difference - go listen for yourself.
If a person is running an inefficient speaker (let's say 85 db. or less) or one that requires significant current due to low impedances in the bass or steep phase angles, then an amp with really stiff power supplies will, all else being equal, control the woofers better. When I write "amp with really stiff power supplies", however, I do not mean one that simply has a high wattage rating - as correctly noted above by several other posters, the fact that an amp has a high wattage rating does not necessarily mean that it has first-rate energy storage, e.g., Audio Research's 600 watt/channel monoblocks have less energy storage than CAT's 100 watt/channel JL-1 monoblocks.
Putting the issue of energy storage aside, there are two major disadvantages to high-powered amplifiers. First, it is very difficult to control a high-powered circuit without global feedback and virtually every high-powered amplifier therefore uses it. Global feedback sucks the life out of music by destroying three-dimensionality and giving it a closed-in, deadened quality, and can create highly complex distortion products. Most triode tube amps do not use global feedback, and well-known solid-state amps that do not use it include the darTZeel (Herve Deletraz HATES feedback), the Ayre monoblocks (Charlie Hanson HATES feedback), the new Rowland 625, a variety of Pass amps, and speaking of Sim, the Sim Audio W-5. Pass has made some very high-powered amps that do not use negative feedback, but most amps that eschew feedback are lower powered (the darTZeel and Sim put out roughly 150 watts/channel into 8 Ohms - the Ayre monos and the Rowland put out 300 watts/channel). For technical papers about negative feedback, see the Pass and Atma-Sphere websites.
The other downside of powerful amps is that they feature many output devices (by "output device", I mean output transistors in the case of solid-state amps and output tubes in the case of tube amps). All of those devices muck up the sound in systems that are otherwise high resolution because, among other reasons, it is very difficult to match output device pairs, every device adds noise, and they make the circuit more complex. For this reason, it is often said that the best sounding amp in an amp line is the lowest powered one. Most high-powered amps use a dozen or more output device pairs, while the darTZeel, in contrast, uses a single pair of transistors per channel. Circuit simplicity is indeed highly desirable - it's why many serious audiophiles put up with 8 watt (or less) per channel single-ended amps that use only one output device per channel.
If a person runs inefficient speakers in a large room and listens to electronic music (anything amplified and then recorded, like rock or pop), then high-wattage, brute force amps are arguably desirable. But if a person has reasonably efficient speakers (87+ db.), a normal-sized room, and listens mostly to unamplified acoustic instruments (classical, jazz), a high-powered amp will, relatively speaking, sound less like real instruments and more like an electronic reproduction.
So, how much difference does a more powerful amp make? It can make a huge difference - go listen for yourself.