The only disadvantage to compress your CSS is maintenance (since your entire CSS file ends up on one line it’s difficult to read/maintain).My approach to this is to have 2 CSS files in your project, one compressed and the other not. I have my code reference the compressed file. When changes are needed I update the non-compressed file, recompress, copy and paste the results over the compressed file.
Of course you only need to compress your CSS files when you move to production.
Here is a link to site that will compress your CSS