Some farriers sharpen their rasps some people use them till there dead and just grab a new one. Depends how much effort you want to put into pushing the rasp. My dad used to sharpen normal rasps, now he uses a new design could a hoofplane which you just round up on the mop, and the finishing rasp doesn't take to sharpening well.
Rasps are good for the feet of wheel barrows if yours keeps wearing through legs