There are some obvious assumptions about how Apple's collection of WLAN Access Point and mobile cell data in a recently publicized database on the iPhone might be good for.
For instance, improvement of location based services by Ap and cell location data. This might be useful for indoor navigation where GPS does not work.
Let me give you another guess:
A few months ago, there were rumours about Apple coming up with SIM functionality built into the iPhone. This would make Apple a global Mobile Virtual Network Operator and bring back the ability to negotiate cut-throat deals with Mobile Network Operators as they had get it with revenue sharing back in the iPhone 2 introduction times.
As we know, data flat rates are rarely profitable these days. This isn't Apple's problem, the quote "New Yorkers like expensive things" applies to all of their customers. However, if you are clever, charging high prices doesn't keep you from cutting cost. So Apple might look at deals with large WLAN access point operators to get their bytes across a little cheaper, if possible. When you have statistics on all WLAN AP MAC addresses an iPhone user has seen, you could get a list of their MAC addresses from WLAN operators, correlate those and estimate the advantage you would have from a deal.
The case against my guess is that there is the database does not store the number of times I came a across a specific Access Point.
Enjoy, and entertain yourself with a guess of your own!