You can sling the guitar wherever works. Like you say, some play with it slung around their ankles, some with it resting under their chins...

What you need to do is find a comfortable position that doesn't strain your wrists. If you try to shred with your guitar on the floor, you're asking for trouble with tendons in my opinion.

I recommend playing sat down with your guitar strapped on, and not resting on your knee. That way when you stand up, the guitar is still in the same place...