<img src="http://blackhornettechnologies.com/Construct2Stuff/BlankEventSample.jpg" border="0" />
Blanks can be used if you need several steps in the same event. Here I set up ProjectileAngle, then alter it based on some limits, and once it's validated, I use a blank event to keep going.
I also like to use blanks just to break up long events, so it's easier to group things together and see the logic more easily/cleanly.
I also use them if I want to make some local variables, where the alternative would be globals.