The wattage needed is really dependant upon a number of considerations. First, lets assume that you have chosen your speakers and you are wondering if your amp is powerful enough. If you amp has needles showing how many watts it is using at any particular time, you can use this information. McIntosh amps have a real neat setting called 'hold' which locks the needle at the peak wattage use. If it never goes too close to the amp's max, you are probably okay.
Still, the question remains, are you over-stressing the amp during just regular enjoyment?
Play your CD that has real loud and quiet music. Certain DVDs and "the 1812 Overture" come to mind. Set the volumn just a bit louder than you like. Watch the needles. If you amp is rated at 100 watts/channel and the needles almost never reach that 100-watt level, you are okay. This does not mean you could be better off with a more powerful amp, it just means that your system is not too stressed by the efficiency of the speakers and overloaded by what you want from it.
Your amp will only 'clip' (especially if it is a tube amp) if there is a mismatch. Of course, with a high end amp like McIntosh, clipping won't hurt it, ---just somewhat shorten the tube life.
Speaking of tube life, there will be a shortening of the life of you amp-tubes if you continue to run the amp at full capacity, or if you like lots of home movies where there are lots of 'loud' noises'.
In this situation, more watts is better as your amp is less stressed.
Now, do watts matter in what comes out of your speaker? Certainly. The bigger question has more to do with what I have talked about above. Inefficient speakers that stress the amp won't sound as good as you are asking too much of your amp.
I am sure some will say my analysis is too simple, but is is a 'good start'.
Still, the question remains, are you over-stressing the amp during just regular enjoyment?
Play your CD that has real loud and quiet music. Certain DVDs and "the 1812 Overture" come to mind. Set the volumn just a bit louder than you like. Watch the needles. If you amp is rated at 100 watts/channel and the needles almost never reach that 100-watt level, you are okay. This does not mean you could be better off with a more powerful amp, it just means that your system is not too stressed by the efficiency of the speakers and overloaded by what you want from it.
Your amp will only 'clip' (especially if it is a tube amp) if there is a mismatch. Of course, with a high end amp like McIntosh, clipping won't hurt it, ---just somewhat shorten the tube life.
Speaking of tube life, there will be a shortening of the life of you amp-tubes if you continue to run the amp at full capacity, or if you like lots of home movies where there are lots of 'loud' noises'.
In this situation, more watts is better as your amp is less stressed.
Now, do watts matter in what comes out of your speaker? Certainly. The bigger question has more to do with what I have talked about above. Inefficient speakers that stress the amp won't sound as good as you are asking too much of your amp.
I am sure some will say my analysis is too simple, but is is a 'good start'.