Visualizing Arcs
In the viewport/3D space:
To see where an a control was on the previous frames, select the control and click the “Ghosting” button on Animation shelf. Turn it off by clicking the button on the right of the ghosting button.
In the graph editor:
Select the curves and click the buffer curves button. This will save a ghost of the curve that is currently there, so when you make changes you can see what it used to be.
Then go to View –> Turn on Buffer