Last year when we put our pool up we didn't do the pad. Right about the time we wanted to close the pool for the winter, we noticed the ground getting wet around the side of the pool the steps were at. For over a week we looked and couldn't find the leak.
Called PS even though we were past our 60 day installation warranty and they sent someone out to find our"two" leaks. One was right at where we had the steps (had already taken them out) and the other was about where the waterline usually is (assuming kids toys on that one).
This year we bought the pad. We had to buy the bigger one. The smaller one doesn't cover where both "feet" hit. We do need to trim as I'm not sure how the auto vac will handle going over the pad that isn't covered by the steps and when I do my normal vacumn, it likes to suck it up.
You may not have to buy the PS pad, but I got tired of looking for something that 1. would fit, 2. look nice and 3. something that would be okay with pool chemistry.