After installing DirectTV at your command center, your CC gets 50 energy, and three new abilities, all of which conveniently cost 50 energy.   1) Scanner Sweep:  Area reveal (also invis units) 2) Call in MULE:  Extra harvester, harvests 30 minerals per load instead of 5 3) Supply Drop:  Adds an extra 8 food to one of your existing supply depots instantly For 150 minerals and a 35 second build time, this is without a doubt the best investment in the game, as it pays for itself within 30 seconds of completion.  I decided to run some numbers on just how good the mule is, and its cost effectiveness in comparison to the Supply Drop.

Read this article:
Blizzard.Com