Circuit allows you to easily specify if you want your route to start or end at a specific point.
Say for example, you build your route from home, but you need to visit the depot to load up first. Here's how you'd do it:
Add your stops as you usually would.
The option to add a start and/or end location will automatically appear at the top and bottom of the list. Tap the one you want to add.
Select your current position or type the wanted address
Finish editing, and optimise the route as usual.