I've ran with a variety of Healing styles as a tank. For the most part I try and click off Regen before a pull.
I've had parties where the WHM never uses Regen and I've had parties where the WHM thought Regen was hot shit and used it like it's going out of style.

Like was mentioned before, the best use is on larger pulls after I flash once or twice and then leave it be, don't recast it. It gets annoying when the WHM casts regen at the beginning of the pull and then again when the last mob has like 2% health left.