To elaborate on Mapman's answer... since tube amps soft clip they can be played at a higher average level since their clipping distortion will not usually destroy speaker drivers (normally tweeters). And many users of tube amps routinely drive them past their clipping points and then contend that "tube watts" are more powerful than "SS watts".
When a transistor amp clips not only is the sound harsher, but the type of distortion produced often will fry tweeters and sometimes other drivers. By the time you hear obvious distortion it is often too late. So greater care must be taken when dealing with the maximum power limits of solid-state amps although I believe some of the Class-D digital amps also clip softly (more like tubes).
With analog solid-state amps it's better to have too much power than too little power so that you never need to drive the amp past its rated power into potentially damaging distortion.
When a transistor amp clips not only is the sound harsher, but the type of distortion produced often will fry tweeters and sometimes other drivers. By the time you hear obvious distortion it is often too late. So greater care must be taken when dealing with the maximum power limits of solid-state amps although I believe some of the Class-D digital amps also clip softly (more like tubes).
With analog solid-state amps it's better to have too much power than too little power so that you never need to drive the amp past its rated power into potentially damaging distortion.