I tend to do it before every delivery. I like the little bit of moisture from blowing in my thumb hole. It allows me to have a very relaxed grip.

Wiping off the ball, I think that might just be a habit at this point. LOL

I don't do the thumb hole blow.  I like my thub to be bone dry.  I hate the feeling like the ball is slipping.  My thumb is extremely tight (that's what she said, i couldn't resist). I do wipe the ball after each shot.  More than a habit, just think if you threw the same shot, same release, same track, the oil flare would be right on top of itself, thus causeing reaction to be diminished.  Isn't that the point of flare?  To have a new, clean, oiless surface touching the lane for max results/friction? 

Wiping the ball is great unless you're looking for the ball to push further.

As for blowing in the thumb hole, I do it on almost every shot. I use rosin, forward pitch in the thumb, and white tape in the back as well. I like to feel SECURE in the thumb, to be able to relax my hand as much as possible.

"Blowing in the thumb hole can help, if your thumb is beginning to shrink but not enough to add a piece of tape. It's not the wetness but the humidity that makes your thumb fit the hole tighter. I wouldn't do it every frame, at least I don't."

Especially with cooler weather the humidity helps get a tacky feel in the ball. It is for when my thumb has shrunk and after some tape is in between on how it fits. Once my thumb starts swelling then I can stop.

Wiping the ball of excess oil after a shot can't hurt.  Blowing in a thumb hole as pointed out, lets you relax your thumb.  More importantly, bowling like most sports relies on muscle memory.  What you are doing is establishing a pre-shot routine. Ever see a basketball player shoot a free throw?  Might spin the ball in his hands twice, bounce it three times, and shoot.  Another does more bounces and does not spin it before shooting.  Point is, do the same exact thing before every shot and it primes your muscle memory for the action, in this case, free shooting.

I come up to the ball return, pick ball up, spin ball three times on towel held in right hand, blow in thumb, grip ball, always look at my focal point, then to my aiming point, and go.  Like I said, primes the muscle memory for your shot and helps cleanse your mind of extraneous thoughts.  Watch the pros, they all use a pre-shot routine.  Try it.  You'll see good results.