I think it's as easy as

F-->T% x 0.T-->R% = F-->R%?

Example:

F-->T: 48%
T-->R: 75%

48 x 0.75 = 36% of hands that saw the flop went to the river.

I think they might be worth knowing in isolation because you could get a feel for whether they are persistent flop callers or bettors (and this may be to chase something because they are bad players or are getting the pot odds, or to see whether you really like your hand by looking at what you do on the turn under pressure, and maybe to bluff you if you're out of position and check). Certainly if the F-->T is high and the T-->R is low, I would (in a marginal situation) pay them less mind on the flop, attack them on the turn, and if they go to the river with you they probably have the best hand (take a look at what quality they have shown down though).

Just my 2p.

Thanks for the math help. One more question, you say if Flop to turn is high and turn to river is low, what would consider a low percentage. You knew that question was coming didn't you?