The points possible settings can be confusing because there are actually two values that can be set. As shown below, you can set both the points and the grading scale.
Points refers to the weighting of the item within your points system. The higher the value you set here, the heavier the weighting on this item will be when students' overall grades are calculated.
Grading scale is your actual points possible for the item.
Generally, is it simplest to set the points and the grading scale equal to one another. However, there may be times when you desire to set them independently. For example, I can choose to score an assignment out of 10 for my convenience, but may want a heavy grading emphasis on the assignment. So, I set the grading scale at 10, but the points at 50 (or higher).