If someone doesn't want to end up in my position with speakers too big for one's room.
1. Then choose the right speakers for the room and their intended placement. Consider front , bottom, rear ported and sealed designs. Sealed designs will always usually work best, but are very inefficient, and will need a powerful amp to drive them.
2. Floor standers vs bookshelf : floor standers are not the solution for every room. For the same floor space book shelves usually are easier to tame in a small or less than ideal room configuration. Book shelves usually have less bass extension than floor standers. If more bass presence is sought, it is better to add a sub later to book shelves. But once we go with floor standers , we cannot substract the bass. So whenever in doubt, start with a smaller speaker than start with a bigger one.
3. Depending on what speakers have been choosen and their efficiency . Then an amp can be decided next to drive these speakers. Quality watts are more important than out right brute power. There are known combinations of speakers + amps that work. So this will give us a rough idea about the amps to consider.
Well I didn't follow rule nos 1&2. So I have these huge speakers with too much bass in my small room. And now iam forced to consider room treatment and dirac room correction. Both additional investments I didn't originally budget for