First to launch on a SpaceX Rocket, with a much higher payload capacity then required, so I believe they are launching it into a more final orbit then they normally do. Lots of precautions as it is the first GPS3, they want it up there for testing so the schedule of launching the second one in April doe not slip.
There are tons of articles out there on it, a quick google search will waste your day with reading.
FYI, SpaceX will stream the launch live and archive it on their youtube channel if you want to watch it. Pretty cool stuff.