Ordinance or Law coverage is a must if you own older building. People often forget that their regular insurance may indeed pay for replacement value of the structure in case of total loss, but the problem is that older buildings are, as a rule, built with less sophistication (for instance lacking fire-extinguishers), using less advanced (thus cheaper) materials and following less stringent building codes in general (to sustain earthquake or flood, to save energy, to protect against radon gas etc.)

Without Ordinance or Law coverage, your insurer will only pay for replacement value of the original structure as it is, without the necessary upgrade. Thus, all the upgrades would go out of your pocket. Building laws and codes are regulated mostly on the level of counties. If your county codes changed significantly since your property has been built, consider Ordinance or Law Insurance.