This is the number of queued billing records that, once reached, triggers the node to place a call to the logging or printing destination to dump those records. An admin tunes this threshold to balance how promptly billing records get delivered against how many separate calls the node has to place to its billing destination; a lower threshold means more frequent, smaller batches while a higher one means fewer calls but more records at risk if something interrupts the node first. For example, setting this to 20 means the node places a call to dump billing records as soon as the 20th record accumulates in the queue, even if the billing timer hasn't yet elapsed.