Just another thing to make you stand out from everyone else really.
But if you aren't super academically gifted but can show you are able to work hard in other ways, i.e. work/volunteer experience, extra-curriculars, etc. then that might help balance things out.
Depends on the degree though.
For my degree, high marks are mainly only needed to get you into research and stuff which will give you some extras for your CV later
but
passing the degree you still get the same job at the end and need to work up anyways, just the high-scorers have a few uni-related extras you have to compete with