When I was a novice CSS programmer, I wrote all my code in a single css file, just a style after the other. I knew that HTTP works better with a single big file instead of multiple little ones.
But soon this file became very large and difficult to update, my system was not modular and scalable.
Then I read SMACSS and it changed the way I architect my CSS source code.
But the modularization of CSS yet caused the creation of multiple files, instead of a big one, with all its implications. So I began to search a tool to concatenate and optimize my files in a single one.