Question about speaker stands

[zicmubleu]

I just read through crackinhedz speakers 101 thread and didn't see this specific topic covered, why are speakers often mounted on stands? Beyond delivering the sound at a more ear height level is there some tonal improvement having the speakers away from the wall or sitting on top of a shelf? Do the stands themselves provide a vibration insulation effect, trying to reduce sympatic vibrations of whatever they are resting on?

Also I saw pictures of some sub-woofer cabinets that are down pointing design. Is this an enhancement for that type of speaker as well? This would seem to imply reflecting the sound off the floor for the sub-woofer is desirable but getting reflections off a wall from the other speakers is not good.