The MQSeries interface can have a number of requests "active" at any point in time, up to the number of licensed Document Processors. Provided that all document processors are running, this ensures that as many requests as possible are handled concurrently. If less are running, some of the "active" MQSeries jobs will be queued at ITP/Server for processing. The latter has consequences for the MQSeries priority mechanism (see below), so we advise to always start all available Document Processors (there is no reason not to).