Greghain,
Check with neighbors or local PB or pool service company regarding the height of the ground water in your area.
If you are draining for water chemistry problems, you can drain all but 2-3 feet if you are concerned about ground water.
The pool shell is like a boat. If the water pressure on the outside exceeds the pressure on the inside it can float.

They pierce the gunite with several holes so that it relieves the pressure and the groundwater (if any) flows into the pool instead of the shell 'popping' due to buoyancy. My pool is in the process of being constructed and it has these 'weep' holes in it as it's going to sit empty for a couple of weeks whilst the rest of the construction (tile, coping, decking) is being done.
When they go to plaster it, they patch the holes up.