(Trying to explain my thinking)
To me this is an extension of the trust you require and the boundaries you jointly agree to in any relationship.
If I share a home and bed with someone, they theoretically have easy access to my most intimate belongings, my journal, my treasured possessions, my private paperwork, my electronic devices. However, I'm a private person, so I would only be in a relationship with someone who I can trust to be in proximity to these things and not violate my privacy by snooping. Other couples have different boundaries, and share more.
Similarly, I would only share a car (which we each use separately, and is often parked erratically, so needs to be located easily), with someone who I could trust to use the tracking to ONLY locate where the car is parked and NEVER to track my movements when I am using the car solo. Just like I'd trust them to never read my journal or snoop in any of my private things (even though they could).
If I can't trust them not to track me in the car, I can't trust them not to read my journal, or email, or, etc, and so the relationship has bigger problems anyway.