My first trauma therapist used to tap me. I thought it was funny and I like it but I like touch. She told me to do it and I tried but I did not find it really did anything.
I haven't tried it myself, yet, but know of a handful of other folks in real life who swear it changed their life for the better in dealing with chronic illnesses and they regularly practice it. Just as anything else in life, different strokes for different folks. If it's a healthy distraction that brings relief and doesn't harm another, rock on with it. If not, NEXT!
I also know people that swear by it for helping with their anxiety disorder. I took a class, but it wasn't too effective on me. I am finding that methods that involve the whole body are more grounding for me. It is something that I might give another shot one day.