Is it possible to reduce Starcraft 2's disk footprint?
If you don't have enough space on your internal drive follow these steps:
install StarCraft 2 on an external drive and once it reaches the first step where it says "optimal" in green you pause the download.
If you don't want to use your external drive every time you play, you can move the install folder now to your internal drive
search in the battle.net client for the Folder where you moved it and resume download but pause at the optimal green step again.
This way you only need about 5gb