When you change your spine angle (either front to back or from side to side) you change your plane. Your spine angle can be likened to an axis. Let's compare the earth and a globe. The globe is on a fixed axis. The earth's axis wobbles, thus the earth's seasons change. We would like to be like a globe and stay in the same season as we turn our shoulders.
Beginning golfers often change their angle because they are trying to use their entire body to move the club and simply do not know how there shoulders should turn. More experienced players get the club off plane and they are trying to put the club in a better position by changing their spine angle. Either way the golfer will struggle with inconsistent shots when the spine angle changes. However, if the club is coming down too steep changing the spine angle will prevent crashing the club into the ground and taking too much turf. Here is a look at the different spine angle positions.
Front to Back
With the front to back, if you lean forward with your spine, the shoulders will turn steeply and the club will tend to swing more upright. Leaning forward will also cause you to be closer to the ball, resulting in hitting in the heel or too much ground. If you lean back, the shoulders will turn more around and the club will tend to swing more around or flatter. Leaning back also causes you to be farther from the ball, resulting in misses off the toe or bottom of the club.
Side to Side
If you lean towards the target, the bottom of the swing will be forward and tend to have deeper divots. Remember the shoulders should rotate 90 degrees to your spine angle so l leaning left tends to swing the club too much outside on the backswing and steeply to the left on the downswing. The bottom of the swing is forward and is characteristic of a slicer.
Leaning right tends to swing the club too much around on the backswing due to the shoulders turning more around. If you lean away from the target, the bottom of the swing would be behind the ball with shallower divots. This position would cause the club to swing on more of an arc characteristic of pushes and hooks.
Correcting our spine angle might not correct our misses as mentioned earlier. Ask yourself why would you change your spine angle? Is the changing of your spine angle the cause or attempted correction for your mistake? Example: If your swing was too steep, you would tend to hit too much ground. In order to avoid hitting too much ground you might raise up with your body. If you raised up the right amount (adding a mistake), then you can get away with a good shot because you cancelled one mistake with another. Why would you want to maintain your spine angle if you swung too steeply? The answer is you wouldn't. People don't swing the club incorrectly on purpose, so without understanding your mistakes you have to do something to fix the problem and that usually means adding a mistake. This leads to inconsistent results. Typically, when there is a change in the swing plane it is followed by a change in posture before the consistency comes.