i’m not a super prolific gamer by any means, but I have 30ish games on PS4, a good mix of indies and triple As, and basically none of them seem to use to touchpad in a way where you couldn’t just use a normal button or a normal button plus an analog stick.
Nothing that couldn’t be a simple button press. I believe you can slide your finger across it in Ghost of Tsushima to activate the guiding wind, but don’t quote me on that.
It’s an odd inclusion on the controller. The only thing I can think of is that when the PS4 came out in 2013, phone games were more prolific and perhaps they wanted an avenue to port those types of games over. Maybe it would help with a built in web browser or something, but even the console UI doesn’t make much use of it.