If you have a subscription to BirdsEye, you can load the satellite imagery on your handheld, and/or also view it in HomePort. The images remain even once your subscription expires. If you load the imagery in a specific folder in HomePort you can "toggle it on / off" by selecting/deselecting the folder where you have the images. This is useful for working on routes.
I don't use the imagery on my handhelds very often. It is useful in some cases, where you want extreme detail; for example, it can help you navigate the maze to the dock at CP1, but in general the imagery appears dark as compared to regular charts. I use BirdsEye imagery most for planning in HomePort.
In some cases the imagery is better than Google Earth, but usually GE is better. I use both GE (viewing my HomePort data in GE) and BirdsEye depending on which has the best images. I just downloaded a BirdsEye image from Florida Bay (croc dragover area) and the image is dated 12/17/2018. I don't know the schedule for image updates.
Note, the last time I checked, if you purchase a new BirdsEye subscription, you must use the Basecamp application to activate your purchase. Download Basecamp (free) and click on the "BirdEye" tab, select "Download BirdsEye Imagery" and you should find an option to renew your expired subscription. For some reason Garmin has not added the same activation process to Homeport. Once activated, you can download/view the imagery on either Homeport or Basecamp.
Greg