Adding total accumulated use time over many days, SMS's or transmits helps keep a reality check on missed transmissions. When the time_in_use is correctly set to zero after each transmit, it leaves no history to verify. An example: if I miss the SMS from last night, I do not know if the pump worked. If I have an accumulated time_in_use count as well, I can average that time over two days. At least I know the pump worked.