Before changes to the CSS would happen rather quickly but not immediately. So you would see the the non-adjusted version for a tenth of a second before the changes were applied. Now you will just see the correct format.
One unintended consequence of loading the css higher in the document, in head, is that you may need to be more explicit with rules or use !important to override css that shows up later in the document.
See the green theme example: https://matrix.gvid.tv/c/customcss/F86ocUPCpK