What exactly does the Arduino Template Express do for Atmel Studio

Hi guys,
I plan to use Atmel Studio 6.1 to develop my program for the arduino.(Mainly for the autocomplete as well as navigate to features). While going through some tutorials I realised that we have to install Arduino Template Express - Installation | Omar Francisco to actually get Atmel Studio to recognize the Arduino template? Why is this? What does the software exactly do? Lets say I want to use another library which is not supported by the installer, then what would I have to do? Also how good and reliable is atmel studio 6.1 for arduino development?