Erm, no problem if they're listening exclusively to compressed music (heavy metal, e.g.) at a modest average level at three meters or less with those 86 dBw (at 1 m) speakers.
But lots of music has very significant dynamic range, and 100 watts won't cut it with 86 dBw efficient speakers at common listening levels and listening distances.
A measured crest factor for recorded music of 20 dB is not unusual, and 30 dB is possible with live acoustic music.
A 20 dB crest factor means that the 100 watt amplifier is clipping badly at an 80 dB average listening level at 3 meters into those 86 dBw speakers. A 30 dB crest factor and those speakers need over 2 KW at a 3 meter distance for an 80 dB average.
People listening to little, inefficient speakers often fail to realize just how badly their system is compressing their music, until they hear the full dynamic range properly reproduced on large, efficient speakers.
However, I completely agree that just listing SPL levels for different music types is meaningless. In fact, I'd say that the list Darth Vader posted is nearly
inversely correlated with speaker efficiency and power requirements. Rock and heavy metal is heavily compressed, with a crest factor as small as 3 dB, while classical music can approach 30 dB and is hence much more demanding on a system (unless you listen at very low average levels. 25 watts is just enough at a
70 dB average level (which means the quiet bits are significantly lower) with a 20 dB crest factor at 3m with 86 dBw efficient speakers).
