It's not so much for knowing where one is going. It's for showing the passengers what the expected time of arrival is, *and* for telling the damn vehicle what traffic warnings to put up. (It only puts up on-route traffic warnings.)
Amusingly, when I told #EnterpriseRentACar that the satnav in the #FurdKuga had failed with what seems like a known manufacturing defect of years-long standing (https://mastodonapp.uk/@JdeBP/115360036753077087) the company rep asked earnestly whether I wanted to switch vehicles.
I explained that I could quite happily get around without it.
One of the trips I did was to Gatwick airport, where I had never been. I just memorized that I needed the M25 and the M23, and did the the rest from reading road signs for a few hundred km. It was an utter doddle. Lumping an old Philips road atlas in the back just in case was overkill.
The only thing that I lacked was a reliable guide to whether I'd arrive on time for the flights.