Are they necessary?  Only if you want more detail in your figures.  I believe they are morphs since they show up on the shaping dial, rather than surfaces, but I'm not an expert on that and there are others around that are.  There is also some debate about how much detail certain ones add to your render, they aren't all the same.  They can add quite a bit of realism to places like elbows, knees, and abdomens for close up work where those areas are visible.

Can you live without them?  Sure.  I'd pick up at least the V6 one though.  Having one for each character gets to be expensive.