You want that off for GPS to work properly. It does nothing to help aGPS, and as your phoen can attempt to use that much less accurate method, you should not use it ever unless inside, in which case you should turn off aGPS when you have "use wireless networks" on.
Sprint DEvice Team has confirmed the cache bug on GPS. The problem is intermitant and depends on usage habits which is why some don't experience it. we all have the bug, it can be masked and not an issue depending on your usage habits.
Apply the fix noted by Jim above. I created it with help form a few of use who knowo our way around GPS. There are other small bugs with Epcis GPS but they are not bad ones.
The symptoms our fix repairs is this: you expreince GPS lock sometimes, but no GPS lock within 30 seconds on other occassions despite being in good view of sky. You install GPS test or GPS status and note oen of the follwoign condtions: a) no Satellties seen (expired almanac still in cache); or more commonly b) Adequate satellites seen, but none or less than four "in use" (expired ephemeris in cache). This is definitive symptoms which our fix will repair