Negative side-effect of combine:
URL() references in the stylesheet break if they are relative to the stylesheet. Example: Revolution Slider plugin comes with its own PNG shadows and a dynamically generated stylesheet that displays a shadow user-chosen shadow below the slider. Combine did a perfect job of including the stylesheet in the Combined file, but the URL reference to the shadow PNG is invalidated so the browser look in the wrong place for the shadow.
Proposed Solution A:
Parse URL() references and copy the assets to folder where combined CSS file is saved.
Proposed Solution B:
Intelligently, modify URL() references in combined sheet to correctly reference the location of the assets relative to the combined sheet location.