I can understand why you would need to track the CURRENT position of a phone. But the only reason for someone to keep track of your past position and keep it on a file is to track where you have been. Why would apple need that? And even if there where a valid reason, why keep it secret?
If I wanted to bet, I would say that Apple is selling the service of tracking iPhones. To who? From marketers all the way to government.
Suppose you want to make a union. And decided to make a secret reunion of workers so that the company does not fire the ones in the meeting. the company then knew that the meeting took place and where. Every atendant with an iPhone would be in danger of being fired (illegal, but companies can make any excuse to do so).
Imagine you decide to excersise your first admentment rights (freedom of speech) and join an activity. If you have an iPhone, Uncle Sam now knows you where there and where you live. So next time you travel you get a special treatment by the TSA.
And how about if someone that happen to work at Apple is also a stalker. Great now the person knows every movement of you.
Many horrible uses for this, specially since its done behind your back.