yup. very correct grif. especially when referring to midrange and highrange speakers (any amplification is probably more power than the deck provides)
well, i really only understand the basics of it, and the principles taught to me for functionality and longevity of car audio.
What I've always been told, by anyone who i consider an expert (people with 10+ years in the car electronics business) is that its always better to overpower speakers... Basically due to what Grif has said above, that it requires the gain's on the amplifiers to remain to a minimum and creates less distortion.
The best technical explanation that i've heard is that low power causes distortion, which causes 'wild flucuations' as grif said, which damage the voice coils and eventually blow speakers.