Watching the Clubhead Go Back is the Terrible Habit
When I was in college, I practiced my swing in my small apartment. I didn't have a big space, but it was enough to swing with my short irons. I couldn't take my follow through, but I practiced a lot in front of a mirror.
As soon as I came home, I started checking my swing. Often, I practiced until midnight. I learned a lot of things about golf swing in those days.
Swinging in slow motion was a really good drill. I still do this very often. I just don't practice until midnight these days, but this drill teaches me lots of things.
My Bad Habit
Havey Penick said watching the clubhead go back is a terrible habit.
When you take practice swings, you might pick up this habit accidentally.
I certainly did.
If you watch your clubhead go back during the backswing, you tend to slide your body to the right. This will cause reverse pivot, fat shots, top shots, slice and so on.
Once you pick up this habit, you might do the same thing on the golf course as well.
So if you have this habit, try to focus on the ball as you swing.
The slow motion drill is very effective, and I recommend it to anyone. But when you do it, make sure you place the golf ball or find the spot that represents the golf ball and keep your eyes on it.
I see lots of golfers take practice swings or check golf swing positions without thinking about a ball position.
But practicing without a ball position in mind won't help you improve because your golf swing changes dramatically depending on where to position your golf ball.