The great John Ervolino always stressed that one must play at least one game of finesse along with the more power-oriented rotation games to become a fully refined player. To Johnny, both one-pocket and straight pool qualified as games of finesse.
I see it Johnny's way, and I think it's worth noting that the finesse part of Shane Van Boening's rotation pool game skyrocketed when he took up one pocket. In the last two years, he's started to play straight pool, too, and his speed control has gone up yet another notch.
When he won the World 9-ball Championship in 2001, Mika Immonen played out of the same poolroom as me, Amsterdam Billiards. He practiced mostly straight pool back then, and the finesse he developed had much to do with his great win at the World Championships in Cardiff, Wales.