intrepid70,
To be complete, there is one other way (that I've read about but never used) for a bazaar buyer to obtain food from a storage yard. If a bazaar needs multiple foods, then the buyer will go out for all of them. If she goes to a granary or storage yard that contains multiple foods that she needs, she will get all of them, even if she goes to a storage yard and some of the food there is not set to "Importing".
Besides the advantages of storage yards given by VitruviusAIA, another is that they are less undesirable. When trade conditions allow, many of us have built cities without granaries. (Examples in the Downloads include my Abedju, Meidum, South Dahshur, and North Dahshur.)
But there are disadvantages to using storage yards to distribute locally-grown food (by setting the food to "Importing to maintain 0"). Sometimes the constant whining about hunger gets on my nerves. In my opinion, the most serious disadvantage is that the trade route to the city which sells the food might close, which would mean that granaries are suddenly required. Also, while having no food in granaries might have no effect on city health (as VitruvisAIA suggested), I'm not entirely convinced. Therefore, long ago I resumed putting granaries in all cities, even when they're not necessary. (When trade conditions allow, I sometimes avoid granaries early in a city's life, to save money and workers, but always add them later.)
If you want to store a lot of food, then a good compromise (usable also when food cannot be imported) is to put granaries "getting" food near bazaars and to put storage yards "accepting" food elsewhere (not too far from the granaries). Some of my cities (Menat Khufu is a good example) have more food in storage yards than in granaries.