I had a pool cage but took it down to build my greenhouse. Now I have what amounts to an indoor pool surrounded by orchids. If you have no screen, you get snakes, squirrels, wasps, bats, deer flies and all the rest. The screen also keeps out snails and slugs. I wouldn't have a pool without one. The greenhouse has large sliding windows with screens and is like an extension of the house. I love it.
Jim