It's not only the pros who do this. You'll see it in any pool room with decent players. They won't do it on every shot, especially not on straight in shots or very short shots, but on longer cut shots and on game determining shots in a one-pocket game for example, the player will stand on the line from the pocket through the object ball and look at the path the object ball will take to the pocket. Heck, I'm no pro, but when a potentially game determining shot comes up in a serious one-pocket game, most times I will sight down the object ball path as I described above. For me, I am NOT trying to pinpoint the contact point, I am visualizing the object ball traveling down the path to the pocket and sort of "memorizing" that angled path as I walk back to get down on the shot.