I have been a facilitator for both MBTI and DISC. In my opinion the value comes when the test results provide a springboard for a series of discussions that result in a better working relationship among the members of a group. I've found that generally younger employees are more likely to find value in the tests because they have less experience in workplace teams and are still discovering their own talents and abilities. For more mature employees, the discussions usually just help them articulate what many of them have learned through experience.
ANY test that attempts to categorize people into 4, 8, 16, or however many groups, ought to be taken with a grain of salt, though, when it comes to viewing yourself through the lens of the category you've been assigned. Some characteristics may be bang-on, some will be totally bizarre, and a bunch will be "well, that sort of is true, but..." The only value, again, is using your results as a starting point to think about your own preferences and behavior.
So my response is that, yes, the tests can be useful, IN CERTAIN SITUATIONS, for many people. Are these tests accurate? Probably not, except maybe in a global sense because a specific individual is just too complex, complicated, and unique to be nailed down that way.
