I believe it is that if you use more than 80% and someone else is using 60%, IF throttling occurs on the network, the person using 60% will have priority over you.

Just to add to this. From the document:

Question #1: Is the CMTS Upstream Port Utilization at an average of OVER 70% for OVER 15 minutes?

    Result #1: CMTS marked in a Near Congestion State, indicating
               congestion *may* occur soon.

    Action #1: Search most recent analysis timeframe (approx. 15 mins.)
               of IPDR usage data.

  Question #2: Are any users consuming an average of OVER 70% of
               provisioned upstream bandwidth for OVER 15 minutes?

    Result #2: No action taken.

    Result #3: Change user's upstream traffic from Priority Best Effort
               (PBE) to Best Effort (BE).

  Question #3: Is the user in Best Effort (BE) consuming an average
               of LESS THAN 50% of provisioned upstream bandwidth
               over a period of 15 minutes?

    Result #4: Change user's upstream traffic back to Priority Best
               Effort (PBE) from Best Effort (BE).