Kelly Sutton has written a post called Deletability and I've been thinking about it all day and how his ideas relate to writing CSS:
By working with code, we see that modularity and deletability are closely related. Properly modularized code is easy to delete.
Writing deletable code is writing good code.
Apparently, this is a common approach to writing software although I've never heard of this concept when taken to the front-end side of things. But! I think it should be a goal for us to have in mind when we’re naming classes or building complex layouts. And after mulling over this idea all day I think that questions like "can I throw this code away easily?" should be a measuring stick for whether we're doing a good job at writing CSS.