The rubber hogs last a long, long time. Probably twenty sharpenings on two firestone diggers wouldnt even slow it down. Other tires have different , harder compounds, so dont know about using them on something else for a prolonged time. Probably still get more than your money's worth out of it.
Just know that you can do way more harm than good if you aint careful. I'm speaking for diggers only, but its not something you can really describe or tell how to do. You can look at another tire and try to make yours look the same, but it aint that easy. Its kinda like doing good straightening work on a car frame, someone can talk all day telling you every little thing and technique to doing it, but until you've put several on the rack and actually fixed them, the verbal instructions do you no good. Any one can do it eventually, but only some can do it well ever.
I showed my son the basics of tire sharpening from watching others, he gathered more info from guys who been doing it for years, and he's practiced at it. I feel like an idiot trying to sharpen tires next to him now. But he still doesnt like to do it, and I gotta bribe him to do mine.

It is a nasty , hot (with all the protective clothes), messy job.
Larry