@soix Got it in one 😁
SETs are where this is most important- they only have about 20% usable power out of whatever they are rated for.
You really don't want any amp to be asked for more than about 50% of full power even on peaks. The harder you work any amplifier, the more distortion you're going to get. That also means that the load for the amp should be benevolent rather than having odd phase angles in the crossover, low impedance or the like that tax amp's capacity. The more distortion, the less musical, since that distortion is likely to be the kind that the ear hears easily!