In addition to what has already been said.
Think about whether you are going to EQ and will therefore need, for example, 3 dB extra headroom for that operation. 3 dB is double the amp power.
Various listening distance and thus more power for the same sound level needs to be taken into account outdoors. Indoors, on the other hand, the listening room functions as a reverb chamber (considering all the reflexes). Thus, the sound level is approximately the same at different listening distances (exceptionally not extremely close to the speaker) in the room. Test it with a dB meter and you'll see. Even a free dB app will do to test it.
Intuitively, one already knows that this is the case. It is enough to walk around the listening room and listen.