These functions allowed you to do commonly-requested actions with select boxes.
For example, you can easily pass values between two select boxes. This makes a nice Windows-style interface for choosing components, adding and removing items from a list, etc. Options are re-ordered as they are added and removed from the lists.
Several other functions are included in the source that are not in the examples. This includes copying items in lists instead of moving them, copying/moving all items, and automatically selecting all items in a list.