It’s important to understand that speakers are very directional. That means they push the sound in the direction they are pointed. For optimal sound quality, it is very important to have the speakers pointing directly at the people listening. In fact, the sweet spot is going to be a position with an unobstructed view of all of the speakers in a system.
Not all sound frequencies behave the same. Higher frequencies are very susceptible to being blocked by obstructions. By contrast, lower frequencies are very persistent. That is why you will usually see tweeters mounted up high, while woofers and subwoofers are usually positioned lower. When providing sound for a large group of people, the ideal position for tweeters is actually above head level. That way, the bodies are never blocking the line of sight between the tweeter and all of the ears of the listeners.
Stereo separation is also a very important consideration. We have two ears and our brain determines the location of sounds based on interpolating what we hear from each ear. Stereo replicates that by using 2 speakers to reproduce sound. Ideally you want as much separation between right and left speakers as possible.