In the Tropico 4 DLC Modern Times, you get a Supermarket: it's like a Marketplace in that it serves as a food-distribution point (so people don't have to hike out to the farms), but can store more food, change the type of food it sells (healthy/junk food), and employs 4 people. Marketplaces only ever require a single worker, and I haven't yet seen people starving because they were waiting in line.
In some Modern Times campaign missions, you start with a Supermarket. Early in a game, tying up four high-school-educated workers in a Supermarket is a waste of educated workers. I usually fire three of them so I can use those educated workers elsewhere, but what's the effect of this on the building's services? Do fully-staffed Supermarkets serve people faster, or have a higher service quality, or serve higher-quality food, or what?