On the GPS module is volatile memory and a real-time clock circuit. When the power supply is removed from the module, and no special precautions are taken, the clock will start at "0" and the memory will be flushed at the next power-on. The result is that the module needs more time to get a correct position and time fix the next time it is switched on.
This time can be shortened by:
The backup with a supercapacitor has enough energy to bridge a 48 hour period of no supply. When you use the 3,6V NiCd cell option, this period is several weeks.