When I'm WHM I try to just use Regen on single enemy fights (like Dullahan in AK & Bosses), mainly just because it's a little extra OOMPH when using Cure. As a WAR I don't mind the Regen so long as I can solidify enmity on the mob first, I haven't had any problems maintaining enmity except when it's cast before the pull. Having both jobs helps me understand the dynamic a little better, I think.

As a side note, thanks for the tip about being able to right-click the effect off, I did not know that.