Another reason to crimp is to reduce powder burning the throat, or in a single shot, the first inch or so of the bore, as the bullet launches too early and the burning powder torches the bore. It causes excess leading as well. Very obvious in a revolver, where it will flame cut the topstrap at the cylinder gap. Bad combination to exaggerate that effect is a light bullet with a slow powder with insufficient crimp.
The number of reloads also depends upon the brand of brass. Anywhere from one to a dozen in a Magnum. With mild loads, years.....