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The header for this section gives some context, it says:
"Your vehicle has electronic control units
that have the ability to store data based
on your personalized settings. The data is
stored locally in the vehicle or on devices
that you connect to it, for example, a USB
drive or digital music player. You can delete
some of this data and also choose whether
to share it through the services to which
you subscribe."
To me this is just referring to data transmitted over bluetooth/usb (NOT carplay/android auto) where storing it locally would reduce the need to index the datasets everytime you get in your vehicle. Indexing every time would delay operations such as browsing large music libraries, browsing large contact lists, etc while the car collected and organized the data. In other words, "remembering" heavy data like this locally (on the vehicle) allows the car to immediately offer the headunit's built-in functionality by assuming the data hasn't changed (much) and pointing to things that existed last time a connection to a specific device was established. In the background it would still re-index and fill any gaps/make updates, but functionality interuption would be minimal, unlike it would be if the car "forgot" the data every single time and made you wait until it was finished.
I keep a 500GB iPod in my vehicles so i can access my large music library without needing cell data. In an old chevy sonic I owned and in my current focus ST, it takes 10-20 minutes everytime I start the car to re-index my iPod's music library before I can browse for an artist I want. By storing this data locally, this would be avoided in a ford ranger.
just throwing my 2 cents in because I know ford isn't going to answer you.