Oh, just about anything, really! I fill low areas, or raise the grade in rocky areas so we can mow more easily. I’ve built out slopes so there’s more horizontal space. Using the tractor bucket to pack down after each drop keeps it firm, or it’ll settle on it’s own after a few months.
I DON’T use it in sacrifice areas, though. It holds entirely too much moisture, and turns to mud. Need a rock product for that.
Winging it is reasonable! If you can split your pad into two, being able to move the entire pile over is nice. You get lots of air into it by doing that, really speeds things along. I’d look at splitting down the short side, though–13’ deep x 5’ wide, if you can still get the skid steer in there. It’s easier to maintain a tidy pile if your “free” edge is the short side!