When hand drawing animation, it is very important to stay on model as it is easy to lose the proportions or features of a character. The Shift and Trace feature lets you temporarily move a drawing so you can trace it on a new drawing. This is similar to animators working on an animation light table and using an entire character or cut-out pieces of a character and moving it underneath the new drawing to trace it.
Your drawings will not be modified. It will only be moved, rotated or scaled in the Shift and Trace mode. When you turn off this mode, the repositioned drawing returns to its normal state.
If you use the Shift and Trace feature frequently, you can assign custom shortcuts for Shift and Trace operations in the Preferences dialog box