I do it 'cause it makes the ball feel more comfortable in my hand, and I don't have to use as much. When I put tape in the front feel like I have to use more and it will eventually make you span alittle longer, 'causing you to hang in the ball (in my opinion). But the only downside I found is the back of my thumb get alittle raw from the tape so I use the Turbo tape on the back of my thumb to keep that from happening. Hope this helps, if you have anymore questions PM me
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"It would be nice to have a bunch of babies and just abandon them somewhere" -Dane Cook

Thanks.  It's good to know there are at least 3 people besides me who do this.

:-)

Also kind of wasn't only about the tape, but am (or was) concerned about the ball's drilling...

The night I bought the new (used) ball, it felt great, but a tiny bit too snug in the thumbhole, so during the course of the evening (was in league) I asked the driller to open up the hole a bit more. He did so in baby steps, and finally it seemed ok, but then the evening (and my evaluation of the fit) was over.

Fast forward to this week (where the weather had changed from warm and humid to cool and dry, and I had bowled many more games than usual, causing my thumb to grow, yet the skin to be very dry and smooth), and the ball felt way too loose at first. Then I started adding tape and despite the fit becoming tighter, the ball still wanted to come off my thumb prematurely.

I once had a [different] driller "copy" a ball, but for some reason change my thumb pitch from zero to slightly forward pitch (without telling me). So, I was getting very concerned that the driller hadn't truly matched the other ball.  I asked him if he copied the pitch also (though I didn't actually have him compare with the other ball) and he said yes.

He suggested adding one more shorter piece of tape a little farther down the hole, and I tried it, but felt no noticeable improvement---and the fit was really tight too tight even for someone like me who prefers a snug thumb. Then... in desperation, I took all the tape out, and put one piece in front and one in the back, and was much better.

Course, by now, it was the middle of the 3rd game, and my thumb was kind of raw, so will have to wait till next week as the ball is sitting in the locker at that house (am in multiple leagues, but not back at that house for a week).

My main concern now is that the fit of the ball COULD still be off and I'm just masking the symptoms with the tape at the back. But next week, I'll start off with the ball as is (tape at back), and hopefully get conclusive enough results to where I know the thumbhole is fine as is, or needs to be slugged and redone.

I have occasionally had to put tape at the back of the thumbhole in my other balls, but is rare, and knowing those balls are already drilled to my satisfaction, there's no worry factor or over analyzing.

Anyway... sorry for going off on a tangent there.

I'm the opposite of most people.  I like a tight, but very smooth thumbhole.  I use black tape (Frankentape actually, love how thin it is for fine-tuning!) all around my thumbhole.  Front, back, even sides.  I also use Vise Hada patch on the back of my thumb to help with the clean, consistent release.  I RARELY can use white tape, it makes my thumb hang up in the ball even if the hole feels loose.  I can only use it on those days when for some reason I am just dropping the ball like crazy because it's very cold in the bowling center or something.