I've used fear of regret as an impetus towards action, before. I've regretted the path not taken before, especially in regards to talking about my feelings with women. I've also regretted some of my actions, which makes me not want to repeat them. I think it's a powerful feeling that can work well to motivate you to change future actions, so that future suffering is avoided.
For me, avoiding regret and being honest typically lead towards the same action. I prefer to strive towards the latter, rather than the former, of course.
I don't think I've ever used it as a reason for inaction - apathy has this covered enough.
Edit: can actually think of a few instances