Actually Jacqui
Everyone used to say dont empty the pool for two main reasons.
1/ People (especially kids) may fall into the empty pool.
2/ It was badly built and leaked a lot when it was in use. This means that when empty, the water vin the surounding earth is very heavy and often causes it to collaps.
The main problem is that when you leave the pool full it will go green or black is not looked after, most people don't want the expense during the winter.
Being a Hotel Engineer we sometimes emptied it but put fencing around it, or leave if full but continue to maintain