Ask HN:What is the function of a program manager

I work in a large silicon development company. There are a large number of program managers in the org who do absolutely nothing other than aggregating others weekly reports and repeat the same in conference calls .This keep them occupied for about a couple of hours a week and they are completely free rest of the time . However they are felt to be indispensable by senior management we have one PM assigned to every project. I dont think my org is an exception. What could be the business reason to have such positions that can be done better by a script. What should be the actual responsibility of a PM