Disclaimer: I have never tried this (but now I want to!)
[TL;DR: I think of this like a see-saw on a playground, where the equivalent of its fulcrum is your forearm, if you're holding the blade flat. The longer the see-saw, and the wider your rubber, the more minute control you have determining its degree of roll.]
My opinion, as a penholder, is that the extra rubber (not just the fins) would give you more torsional control since you need to apply slightly more (torsional) force in order to move the extra weight of the rubber. The extra force on your fingers and wrist is very slight (increasing "touch/feeling"), and combined with the small extra weight, you don't "sweep" through the torsional movement as quickly. You're essentially forcing the forearm rotation to move slower so that you can extend the brief time for which you get to "feel" the ball. The
very slight (decreased) change in horizontal arm speed (from the extra weight) would be well worth the extra mental time, or feeling time, which you get on the ball. Furthermore, the extra weight of the rubber may make up (and probably does) for the force which is lost from the decreased arm speed, and therefore, the ball travels at a similar rate as before, but the movement itself was executed in an easier manner.
I think the reason why blades are not built with wider wings (which would be an equivalent assumption) is that doing so would worsen its performance for most other (modern) techniques besides flipping, as blades are subject to some complex physics regarding elasticity and other things:
http://mytabletennis.net/forum/forum_posts.asp?TID=60725&PN=1
Practical restrictions on blades, such as head sizes, may also be the reason why we see so much extra rubber on the rest of the blade, since it is a way to add mass, and therefore force and ball speed, to the whole paddle without compromising its performance (once again, in regard to elasticity).
...says the armchair physicist.
Might be a similar thing.
