The main advantage for me is the injection morph system - I found V2 in Poser4/5 too slow - saving times, loading times, and too large in files - a single figure scene taking ten meg was putting a very large strain on my hard drive of the time. Having said that, the SAE version of V3 negated most of that advantage with the preinjected expresions, and P6 removes it by allowing me to create a version of V2 with external PMD morphs - much quicker, and (for me) much more reliable.