I was watching the golf on Friday. Tiger was hitting his second shot into a par 5. He had 257 to the flag, into the wind. His ball landed on the green and rolled 1 YARD to the right of the pin!
The math on that shot says that he was less than 1/4 of a degree off-line - arctan (1/257)! (assuming he was aiming at the flag). Obviously, he isn't that accurate on every shot as he missed the cut. For that shot though, he was damn near perfect.
For a 300 yard drive, if they are just 2 degrees off line, that tranlates into a miss of 10 yards. As some of the fairways are only 20-30 yards wide, that's not a great margin of error.
On that shot where he hit it in the bush and didn't apply the rule properly and was assessed the penalty, he was say 30 yards off-line on a 280 yard drive - still only 6 degrees! Even that shot that Rory hit behind the bleachers was say 30 yards off line on a 265 yard shot - (arctan (30/265) = 6.5 degrees).