Awkward chunks of whitespace—typically passive leftovers created when dealing with the important elements on the page—distract & detract from a well-resolved design.
The 5 second test.
How do you know if you’re suffering from lumpy whitespace? Open your design and look at it for 5 seconds. If a section of negative space jumps out at you before your eye locks on meaningful content, you’ve probably left some space unresolved.
The grid will save you.
Weird rivers of white are often the result of deviating from your grid. Align everything in columns to the left, top and right of your design, and you’ll probably see the whitespace sort itself out naturally.
Everything should always be aligned to something, vertically and horizontally, unless you’ve made a very conscious decision that it shouldn’t.