Both of those assessments are most useful as a source of self-knowledge, and are often more useful when you're in a situation where you are not being true to yourself, or have lost touch with some aspect of yourself that needs to be revisited. For instance, if you're in a job you hate but you don't know why, Myers Briggs can be really useful to help understand what aspects of yourself may not be a fit.

If you haven't found them useful, it could be that you're already in an environment that's a pretty good fit for you, so those a-ha moments aren't as necessary!