In terms of self understanding, I find that using Enneagram in addition to MBTI helps give me a more complete picture of myself than either one would alone. I think that taking other personality tests might be helpful in this as well. Each test giving me another piece of the puzzle or showing another aspect of myself.
I am looking at the sub-forum for on-line tests. Some of them, like "what supervillian are you" are clearly just for fun and don't really give you any insites into your personality. Others, like the value sorter or what type of thinker, could potential give insites.
How do you judge what is a good or useful test and what is not (excluding those that are obviously just for fun). I mean I could make up some categories and come up with some questions I think define it and slap a personality quiz up there. Ideally the tests would have some kind of psychology or logic or something behind them, but I can't really tell if they do or not.
So do I take them and then see if they seem valid based on how the results fit? Do I just regard them as all for fun and not view them as anything deeper? Do I look at various results and see if they form a pattern?