They also clear up a long-held medical falsehood: old food almost never makes you sick, contaminated food is what will land you in a hospital bed (or grave). So, these dates, even with fickle dairy items, are not safety precautions. Deli meats, unpasteurized dairy, smoked seafood -- these are the foods that may increase in contamination with time. Graham crackers? Not so much.
Expiration dates signify freshness and taste
...and not some mystical time where your food will "expire." But "freshness" in this case is a nebulous, unspecific parameter.
Once dates on packaging became industry standard, the government began to pursue a uniform system for marking freshness dates. There was zero federal regulation and standardization of dates placed on food. The FDA even attempted to gain some control, but since the labels focused on freshness rather than health, they determined it was not worth their precious time.