If you are talking about the V4 figure (as opposed to Genesis) then this figure was not designed to require subD—it's a reasonably high resolution figure at base. I wouldn't have thought that subD wwould benefit at all; however, if you find an improvement by using a level of subD, that's fine, but I'm sure you are right that it will not look any better with 2 levels.

Obviously, with Genesis one level of subD is essential, but I don't see any benefit in turning it up higher*. On different kinds of models (e.g. some props) it may well be a different matter, although many props don't have appropriate geometry for SubD. On the other hand, I often add a subD modifier to clothing, usually when fitted by Autofit, and I find that very useful sometimes.

*The exception to this is for prepping figures for rendering in Luxrender (e.g. via Reality), where turning sub D to 2 or 3 levels can eliminate "grazing" artifacts (they look like parallel lines on the skin) which occur under certain lighting conditions. As I only use Luxrender I always set subD on Genesis to 2 before rendering.