In other words, I'm given a strong key that is very difficult to break and I use it to either hide or expose my identification with the tracks. In addition, if I choose, I can use my key to remove all of my tracks from the database, if I wish.
The intended benefit is two-fold:
1. You may have gps tracks but you can't know who I am unless *I* allow you to know.
2. I may decide that at some point in the future, I don't want my passive tracks to be used as part of the database.
The downside would be that if you upload tracks to the database and some time passes before you decide to remove them, they *might* have been used or even duplicated by someone with legit access to the database. Although that pool of people is probably small, you don't really know for sure what it might be in the future.