This functionality allows users to compare the current calculation of your route (Google Maps) with the calculation of another map (TomTom for example). When hovering your mouse above this function within the Toolkit, 2 other map types will appear. Clicking on one of the maps will compare that route calculation with the calculation of your current route.
In this example we'll be clicking on TomTom. The comparing process will therefore be between Google Maps and TomTom. Here is the result:
The black line is the original route. The (lime) green line is the route calculation by TomTom
A good tip for comparing route calculations is that when you enable toolkit functionalities within the other map types, these changes will be carried over during the route comparing process. For example: You've created a route using Google Maps (Black line) > Next you switch your map type to TomTom > In the Toolkit of TomTom for example you click on 'Windingness (high)' > You then switch back to Google Maps and click on 'Compare route calculation with TomTom' > The green line that appears (TomTom) is adjusted to be a route with Windingness high because of the changes you have enabled in the TomTom Toolkit. This type of comparison can be very usefull when you want to take over special toolkit functionalities from one map type to another.
A second tip is that you can compare your route to 2 other map types at the same time.