I have read a couple of posts of people using balsa strops. In all cases they used some sort of stropping compound. Is this the main use of a balsa strop? Why not use leather instead? My guess is that balsa is harder, so it can be more abrasive. But do you use a leather strop afterwards then, or does the balsa polish enough already?

As you might infer, I am slighlty confused . When to use leather and when to use balsa?