I use the back buttons in Deep Rock Galactic to mirror the A B X Y functions. This allows me to jump for instance without taking my right thumb off of the stick. I have found this is super useful as I can be steering my POV while jumping. Took a minute to get used to but now I absolutely love it.

Rock and Stone, miners!

I pretty much never use them, don’t have the right hand shape and grip for it.

Some games have button layouts that make certain actions a pain. Two examples.

Horizon Zero Dawn - Healing is by default done by hitting dpad up. You generally want to press this button whenever you take damage to essentially trigger health regen, but doing so requires taking your thumb off the left stick, which means you can’t simultaneously avoid even more damage. Bind to back button, problem solved.

BallisticNG - Weapons are bound to X, discard weapons is bound to B, and accelerate is on A. So when you pick up a weapon, to discard/use it you either have to drop thrust (bad, never do that) or awkwardly shimmy your thumb to either hit X or B without letting go of A. Bind X and B to back buttons, problems solved.

In games that don’t have good auto-save (like Skyrim), I’ll map one of the back buttons to quick save.

In games where combat uses the bumpers a lot I bind the back buttons to that. For the rest of the games it depends on the what I find annoying to do repeatedly and end up mapping that to a back paddle.

For example on Breath of the Wild the back paddle was run which allowed me to run with one hand.