Based on my personal general definition, GPS is a tool for us to found out where the location we currently at.

The Global Positioning System (GPS) is a space-based global navigation satellite system that provides reliable location and time information in all weather and at all times and anywhere on or near the Earth when and where there is an unobstructed line of sight to four or more GPS satellites. It is maintained by the United States government and is freely accessible by anyone with a GPS receiver. In addition to GPS other systems are in use or under development. The Russian GLObal NAvigation Satellite System (GLONASS) is for use by the Russian military. There are also the planned Chinese Compass navigation system and Galileo positioning system of the European Union (EU). GPS was created and realized by the U.S. Department of Defense (DOD) and was originally run with 24 satellites. It was established in 1973 to overcome the limitations of previous navigation systems.

More information: http://en.wikipedia.org/wiki/Global_Positioning_System

Based on my personal general definition, A-GPS is a tool for us to shorten the satellite locking period (access to GPS satellite).

Assisted GPS, generally abbreviated as A-GPS, is a system which can, under certain conditions, improve the startup performance, or TTFF (Time To First Fix) of a GPS satellite-based positioning system. It is used extensively with GPS-capable cellular phones as its development was accelerated by the U.S. FCC's 911 mandate making the location of a cell phone available to emergency call dispatchers.

Moe information: http://en.wikipedia.org/wiki/Assisted_GPS

A point of interest, or POI, is a specific point location that someone may find useful or interesting. An example is a point on the Earth representing the location of the Space Needle, or a point on Mars representing the location of the mountain, Olympus Mons.
The term is widely used in cartography, especially in electronic variants including GIS, and GPS navigation software. In this context the synonym waypoint is common.
A GPS point of interest specifies, at minimum, the latitude and longitude of the POI. A name or description for the POI is usually included, and other information such as altitude or a telephone number may also be attached. GPS applications typically use icons to represent different categories of POI on a map graphically.

More information: http://en.wikipedia.org/wiki/Point_of_interest

Depend on your need.

If you are only trying to search for a certain location or browse map, not purpose to navigate, then I would suggests you disable A-GPS.
Why?
This is helping you to avoid get charge by Telco Company. A-GPS will cost you around +-10kb data usage.

If you are purpose to navigate, then I would suggest you to enable A-GPS.
Why?
Enable A-GPS will help you to shorten the satellite locking period. In clearer way, means shorten the time to know where the location you currently at.
By enable A-GPS, we able to lock to satellite within few sec. (depend on location and situation)
Without enable A-GPS, we might take a long period to lock to satellite. (if the signal of your location is low). Sometimes it might take you few minutes, an hours, or even unsuccessful lock to satellite.

apps. > Location > Positioning > Positioning Methods > Assited GPS > Enable/Disable

Apps. > Location > Positioning > Positioning server > Positioning server use > always ask