Let me lay out a perspective, casting runes, tarot, etc.. can give a subjective insight into oneself.
It is (near)impossible to predict yourself accurately by setting up a set of rules describing how you would act in a given situation.
The reverse is also true, you can't afterwards conclude accurately of everything why you did it.
We feel things that aren't always purely rational or seem to have a deeper cause than what is apparent.
If you take those three points to be true then you can conclude that feeling something might in fact be a better way to find out why you feel what you feel. So in order to do so you would need a tool or method to guide you as otherwise you're not accomplishing anything. I would then argue that the mystical can because of its nature bridge the gap between feeling and understanding quite effectively at times.
It certainly isn't ironclad but I just want to offer an perspective, or well how one could perceive the mystical to be useful and why one might practice it.
To see just how destructive similar practices can be
That's quite a dangerous way of thinking in and of itself, most things(if not all) taken to its extreme can be destructive.