CSSes are normally cached in the browser. But it not always true. So, if you write a lot of spaces in your css, it may leak out the transfer of unnecessary blank or unreadable characters within the files, for no worth. I had to compete this case.
I dealt with a challenge of the both: Now I can let any designer make css files with whatever blank spaces for formatting of the css lines and comments. While displaying this, I strip off the not-needful formatting and make the css as a compressed file. So, both are happier now: The browser and the designer.