said by Nezmo:Well, they seem somewhat self-explanatory.
Cell network search - not certain.
AT&T still has parts of the old cingular network as well as the other networks it gobbled up somewhat separated from the original AT&T towers. They identify differently to your phone even if all you see is AT&T in the top left corner. GPS location helps the phone know which towers are likely to be local and thus doesn't have to spend as long searching for nearby towers. It speeds up a search, say, when you get off and airplane and turn your phone back on.
said by Nezmo:Compass calibration - the compass occassionaly needs orientation. Perhaps turning this off saves power?
Magnetic and true north are not aligned. The apparent inaccuracy in your compass will depend on your latitude. If you have the compass set to true north, it will take a GPS reading to ensure it's pointing at true north based on your location. Would be activated by the compass app, but also the maps app if you orient the map to match the phone's direction.
said by Nezmo:Diagnostics and usage - not certain.
As another poster added, this is for crash reports and other data, and attaches your location to the report, helping the programmers on the other end identify if perhaps, say, a tower is faulty, not the OS.
said by Nezmo:Location based iAds - I would guess this stops iAds knowing your location. Again, a power saving if off.
Yep
said by Nezmo:Time zone - allows the phone to search and detect time zone.
Yep. So if you travel it will automatically change the time, even if you are outside of cell network range.
said by Nezmo:Traffic - allows the Maps app to search the traffic servers.
This is the only one that puzzles me. Shouldn't the map just show the traffic for the map section you are currently looking at? Why does it need to know where you are? Maybe it caches traffic info in the background in case you open the maps app, or maybe it submits data about your speed and location to a public database others use for traffic information.
Of all of those services, location based iAds, Time Zone, and diagnostic would be the ones most likely to poll in the background while you aren't aware. The rest would only come up when necessary and you'd probably find the phone a little less usable if you disabled them, I'd think.