The only reason to grind a small mirror is because you want a very large mirror and need to practice first. This has long been the case, but the definition of large has gotten larger over time. Of course there is also the in between states where you buy a cheap workable mirror, and then make it higher quality. Unless you have a lot of land high on a mountain there is rarely any point in mirrors that you have to completely grind yourself - the telescope wouldn't be portable and the nearby light and atmosphere pollution means large sizes don't gain enough. (if you do live in such a place your telescope could be massive if you have the years to dedicate - can I come by and look through it one night after you build it?)