As most people already mentioned:
Vendor prefixes which shouldn't even exist as using their non-prefix version should work for all the browsers.
Having to use SASS/LESS or any other SCSS libraries to do stuff that should be possible within the native CSS even if a new version should come to support this.
More control over forms, scrollbars.
Removing all the bullcrap that IE impose to be able to render the CSS well enough like "!important".