What is the point of stars in Mario Kart 8? [duplicate]
They are used to mark 'favorites' in MKTV. If you completed a race that was particularly eventful that you want to save for later, mark it as a favorite by starring it at the end of the race. It makes it a lot easier to find the ones you want to keep, rather than going through all your recent races.
You can keep up to 6 favorite races at a time, and can edit or remove these favorites in MKTV.