Satellite overlay has many benefits whether its getting a good overview of a marina you may be entering or finding good fishing spots in a back water they may not be mapped very well. there is a couple settings you can pic from to help you dial yours in just the way you like it.

Set your display
Satellite overlay can be displayed on land only, land and shallow water or full overlay.
you can also Adjust transparency
The transparency can be adjusted so that Navionics charts are fully or partially visible through the satellite overlay. This is helpful in shallows waters such as marsh areas or shoals and sandbars.