Does this mean the butt intersects the line at a 90* angle or that you attempt to move the butt in the direction of the line?
One of the worst things one can do is to think too much about their swing while they're swinging.
It is more effective if you let your swing manifest your natural body mechanics.
The most important secret to hitting the ball well is keeping your head locked in position. To this end, having a caddie will shave a ton of strokes from your game. Everyone wants to instantly look up to see where the shot has gone. It is far better to follow through with your head still locked in position. Impossible to do without a caddie or a golf partner that you work as a team with watching each other's shots.
The other key is to realize more than half your shots are at or around the green. If your short game is good, you will score well. And IMO, thats the easiest to work if its off.
Couple more things...
Hitting the ball straight is 1000 times better than hitting it far.
Great quote from one of those old-timers... "swing half as fast to hit it twice as far". So true.
So work on the short game, don't think too much, keep the head locked and don't follow the shot with your eyes, slow your swing down, focus on a straight shot not a long shot, and let your body's own rhythm and natural mechanics dictate your swing, not some instructor's idea of a proper swing.
I don't play anymore... but I did.
"Competitive golf is played mainly on a five-and-a-half-inch course... the space between your ears."
- Bobby Jones