That is to say, does the hardware itself do any periodic updating/searching for satellites, etc, if there an no running apps which require GPS information?
If so, what sort of effect does it have on battery life?
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Most phones tend to cache your location periodically and use this information when requested by you applications so that battery drain isn't a big problem.
I believe this is called assisted GPS.
This does have the disadvantage of allowing to your location to quickly become inaccurate. Imagine if your location is cached as you get onto a train, you then you take a photo at the next platform, but your location wasn't updated, the location stored in the image could be miles out.