Vigoras is mainly used in teams that provide a lot of mitigation through Barriers and have a consistent strong amount of heals available, since, as Slashley said, you wanna stay topped up at pretty much all times.
Other options are Burst-focus builds that finish a fight in a couple turns, as you wont take to much damage usually and you also use them mostly during BT, so the biggest value is right of the bat in your opening burst.

Vigoras is a high risk high reward option, but you wanna only take it in combination with something else and not as the sole skill on a weapon. If you can make use of it, it is nice to have, if not, you just better stick to Assault or Pride weapons instead.