When you enter a meter reading, MainBoss attaches a date and time to the reading. The date-time is specified in the "Effective Date" field. By default, this field's value is set to the current date and time.
So consider what happens if you enter two or more readings for the same meter without remembering to set the "Effective Date". (You might do this if you make a typing mistake on the first date.) For example, suppose you enter that the reading on a car's odometer is 30,000, then five minutes later, enter that the reading is 31,000, but you use the default "Effective Date" setting. MainBoss thinks that the car has gone 1000 miles in five minutes. Therefore, if some job needs to be done every 3000 miles, MainBoss will think that the job should be done every 15 minutes, because that's how fast the meter seems to be changing. You'll end up with a gigantic number of expected work orders.
(In fact, MainBoss only generates a maximum of one work order per day, no matter how many times a job comes due on that day. But in the preview or the generation list, you see many many potential entries.)