The tour pros don't have the line on the ball for alignment. They may use it for that, but not why they have it. They have the line on the ball to make sure it doesn't wobble. The ball not being struck properly can cause pace problems. A wobbling ball can take 6"-10" off of pace.
By the time the ball wobbles, it's too late to do anything about it. Not sure how that is helping them, other than to know to correct it on the next putt.
At their level, I would have to think they know how well they hit it based on contact. But maybe I'm wrong.
C'mon HH. There is no way in hell tour pro's have the line on the ball to check the wobble factor. Ok, maybe Bryson Dechambeau does, but he's a nutcase.
I could just see a pro being pissed that he made a putt but the line was wobbling.
Haney was also talking about this on his radio show the other day. Said the same exact thing. I will adjust my original statement because I am sure many do use as an alignment aid as well. It is going to depend if you are a line putter or a spot putter. Still, many will glance to see if they putt a good stroke on the ball which the line helps in determining.
I like the line. Once you're over the ball you can just visualizes a T-Square strike. It helps you to build a consistent stance around the correct target line, and can also help to keep your eyes nice and quiet by giving you something specific to focus on.
Did you watch the video link? I though it was very interesting that he said everyone should line up differently according to how their subconscious evaluated the putt. Most teachers teach eyes above the ball, but that doesn't work for everyone.