When I first started, I promptly replaced the stone wheels on my Rikon 1/2hp with 80 and 360 grit CBN wheels. Originally, I thought reshaping was going to be a common thing, hence the 80 grit wheel. In practice, once I had all the tools I needed, the only thing I ever did was sharpen. So the 80 grit basically sits unused, and I spend the vast majority of my time on the 360 grit. I wish now, given hindsight, that I had purchased what a few had recommended at the time: the 360 grit and a 600 grit. The 360 does an ok job sharpening, but, it still leaves a bit of a jagged edge. I'm not talking about the burr, you can take the burr off, and you still have a very slightly jagged edge. At some point here, funds allowing, the 80 will be replaced by a 600 grit.
For some, this may be a matter of preference and turning style, I guess. At this point in my turning game, I really would prefer a ridiculously sharp and finely tuned edge to my gouges and skews. The edge I get now, leaves small ridge marks in everything I turn. If I spend a LOT of time honing that edge and remove the burr, leaving just a super clean cutting edge, then I can get what I want...but, I don't really want to be spending that kind of time every time I sharpen, since I tend to sharpen several times a project. The 360 grit wheel definitely gives a good CUTTING edge, it cuts really well on all but the harder woods, it just leaves those little ridges.
If this is not something you care about, or if you intend to be making your own tools out of bar or rod stock, etc. then the 80 grit is a fine choice and may even be a necessity. If you just plan to sharpen tools that are already shaped, then I'd grab a 360 and 600. The 360 is coarse enough to re-shape the edge to a fair degree, even if you get an accidental metal catch (I've had a couple, with a couple marks in my live center to show for it!) So its not like you cannot reshape with a 360. I wouldn't use it to create brand new tools out of base metal stock, though....the 80 grit would be best for that.