On the deck I use them all the time. For FPS games I frequently bind them to be ABXY, lets you jump/reload/etc without having to take your thumb off of the joystick. Absolutely mandatory for games like Doom Eternal and Deep Rock in my opinion.

In games with heavy dpad use for cycling abilities/items (like Elden Ring) I usually use them for that. Being able to cycle spells or potions while running is very necessary sometimes. You can also use them in combination with mode shift settings, things like while I hold R4 down it will temporarily turn my ABXY into a second DPAD.

You can use them for steamOS features, stuff like opening keyboard or toggling zoom for games with small text.

A lot of people dislike clicking thumbsticks, so it’s common for people to use them for that. L4 to toggle sprint instead of L3 is very popular for example. Also nice for when L3/R3 do something you don’t want to trigger accidentally during combat (Ys 8 and 9 toggle a minimap overlay with L3, which is very distracting during combat. So I’ve disabled L3 on the thumbstick and instead have L4 open the minimap overlay).

In any PC game with more inputs it can be great for common button presses that didn’t make the cut onto the standard controller. Things like map/journal shortcuts, quick save, etc. Setting left trackpad to a touch menu is also great for this.

Overall they’re pretty great, I don’t use them in every game, but there are a lot of games I refuse to play on a standard controller without them.