Here's an example contra dance hall:

What's wrong with this picture? It's going to feel way louder near the speaker than farther away:

closest person:         1ft
farthest person:       15ft
effective difference: ~15x

This wouldn't be so bad if people could sort themselves in the hall based on the volume they prefer, but contra doesn't let you do this. To get a more even volume distribution, get the speaker up above the dancer's heads:

Now the difference is more like 5x. What if we get the speaker even higher?

This does better because the speaker is now closer to being a consistent distance from people's heads (~3.5x), but it starts to sound pretty muddy. The problem is that a lot of the sound is bouncing off of the ceiling on its way to the dancers, and things sound clearest when you have as little reflection as possible. Additionally, there's a bit of a "hole" right in front of the stage, where dancers will get very little direct sound from the speaker.

To fix this, we can angle the speakers down a little:

Now everyone is happy.

(I've generally used ultimate tall stands with K10 speakers that have a built-in tilter. With speakers that don't have built-in tilters it's possible to use external ones (like these) but they shift the center of gravity of your speaker in a way that might be a problem on a tall stand. Permanent "flown" installation is ideal, but most of us aren't running sound in a situation where that would make sense.)