How much help is a PhD supervisor if you only see them 30 minutes a month? I often hear from PhD students that they see their supervisor only 30 minutes per month, or 30 minutes per semester even. According to my calculations, this adds up to a whopping 13 hours and 6 hours respectively over a three year period (if there's no contact during the holidays). This is less than the typical amount of contact hours during an undergraduate week of lectures. 

This made me wonder: To what extent does such a PhD supervisor really help you? Even if this supervisor is a star professor, does 6 to 13 hours over a period of 3 years, really help you that much with your PhD? 

To formulate the question differently, let's say you're getting 10,000 education/career points out of your PhD. How many would you get if you got rid of the supervisor and basically had to do it without official guidance?
Your supervisor's job is to be sure you're on the right track, not to do any of the work.  Thirty minutes a month ought to be more than sufficient for that.  Also, the supervisor either takes care of the administrative details or is responsible that someone else does that.  Finally, you appear to have omitted the amount of reading required of the supervisor.

I'm absolutely sure I didn't see my supervisor for 13 hours over the course of my degree, but he read every word I wrote and provided feedback without which I probably could not have finished.