In distributed systems a process often needs to wait for more than one of its peers before completing some action. For example, we may send a request to 5 of our peers and require that we hear back from 3 of them before considering the action completed. Even when the distribution of round trip times for a single request is pretty simple, it’s not entirely clear what the distribution of the aggregate request will be. (To me, at least; maybe if you’re smart or know statistics well it’s simpler.) In any case, we can use a histogram to get an idea of the shape of the density function.