From an insurance point of view, the property/ building owner receives a significant reduction in insurance premium because of the automatic fire protection on site. The company I worked for had a detailed fire protection impairment program requiring the "insured" to notify us whenever a fire protection system was out of service. Depending on the operation hazard, $ at risk, our underwriters would actually purchase reinsurance when the protection was out for more than 8 hours. Sometimes that cost of reinsurance was pasted onto the client or we ate the cost. So a tank supplying the fire protection on site empty for 24-48 hours, someone is paying for it.
NFPA 25 requires internal inspection of the tank every 5 years, not too long ago they required the tank to be emptied for the inspection. So in this case it was not something that never happened, it did occur every 5 years.
About the only time I did not enforce the 8 hour time limit was when the tank was for a secondary water supply, where the tank and pump was a backup to the adequate city water supply.
So who put that 8 hour time limit into the standard....the insurance companies and property owners ( they did not want to pay those reinsurance $$$) who were on the committee.