Whitespace
Jason Santa Maria started his own series of design theory tutorials with Under The Loupe #1: White Space
The title is pretty self explanatory and it’s a good read. I think Ian sums it all up quite nicely in the comments:
If I had to make a white space analogy it’d be the one about going over that dude’s house who has every inch of his living room crammed with old computers and monitors and guitars and so much shit that you can’t even walk around. That, or breathing room.