In a nutshell, a head server's job is to make sure you have a great dining experience, in spite of things stupid passengers do.
We had MacClean as your head server, saw him every night, but never needed his services until the last morning. We had late seating, so our last breakfast was at 8 am. The IDIOTS who has our table for early seating didn't show up as scheduled at 6:30 am for breakfast the last day, but showed up at 7:45 am. Technically, they we not even supposed to be allowed into the dining room at 6:45. MacClean made sure they got their last meal, and since the DORKS we sitting at our table, quickly (within a minute) found us a table to sit at. We didn't get our last meal with our waiter and assistant server, but they checked on us frequently, as did MacClean. First class service even AFTER we had handed out tips.