Some builds in our area use wall foam on every pool. I personally do not use wall foam unless there is a direct need for it. I've also only seen one pool use wall foam on the floors, we left it in place since the previous installer used carpet glue and that stuff dries very rigid, so the floor would have been bumpy if we removed it.
Wall foam is used under the intent of protecting the pool vinyl. This is the main reason I don't use it is putting foam on the walls actually makes the liner more susceptible to damage coming from inside the pool (for example toenails, toys, brushes). Try this simple experiment, place a piece of paper on your table and poke it with a pencil point. It might get a small hole, but it might be okay. Now take the paper and place a piece of foam (or corrugated cardboard for simplicity) under that paper and try to poke it with the pencil again. The pencil will go right through and make a larger hole since the pencil has room to travel.
I have used foam in the past when the metal pool walls were so rusty that they couldn't be scraped smooth enough. In that case the foam protected the vinyl from the rough pool walls.
If you live in an area with underground water do not even consider foam, if you take on water the foam will detach from the pool walls and end up in a bunched up mess at the very top of the pool.
That being said, I will admit foam does feel nice to the touch. Also there have been discussions about wall foam keeping the pool warmer as it acts like insulation between the cold metal walls and the water.
