For versatility I see the point of not getting a long ski. But when I've hit the deep powder, I've wanted a longer ski for better float.
179cm Seth Pistol was a blast EVERYWHERE but when I got into waist deep powder, my experience would have gone from a 9 to a 10 if I was on the 189cm, or so I assume.
Same for my Volkl Explosiv: I'm stoked with my 180cm and have no regrets. I almost bought a 2nd pair just in case these got destroyed. The 190cm would be nice in powder but since most of the time it's trees, chutes, bumps, crud, and groomed, I'm happy with 180cm.
For the huge powder days I acquired the K2 Made N AK 189cm. They were tolerable in groomed, crud, and bumps; tough in trees, but in the powder there were quite fun. They now sit in the garage waiting for another powder day.
(I think I'm rambling here....)