If a site uses upwards of 10gig a day, the CMD_BANDWIDTH_BREAKDOWN (and CMD_API_BANDWIDTH_BREAKDOWN) page can take a long time to calculate. This feature will create a bandwidth.tally.cache file with the tally for all accounts all the time. If the bandwidth.tally.cache exists when the bandwith breakdown request is queried, the cache file will be provided. If it doesn't exist (which should be never after the first tally), then the old method of realtime calculation is used.