In working with a social survey, one of the most pivotal issues is determining the level of analysis. Are you going to be studying individuals, households, or organizations? The level of analysis factors into pretty much everything - sampling, creating well-phrased questions, making appropriate generalizations, etc.
Households are a very common level of analysis. In households, you can get very precise information about social issues, without the added cost and effort of interviewing each and every sampled individual in a given population. A lot of surveys are run at the household level because it is both efficient and yields meaningful data.
One thing that I find interesting is how 'household' is defined. Social relationships are often difficult to disentangle, so it's important to make sure that people are correctly included in a household (or appropriately excluded from it), regardless of the legal or familial technicalities. Depending on the survey context, the definition of a household usually has to do with dwellings and/or eating together. For example, the U.S. Census Bureau defines a household as "all the people who occupy a housing unit" and then goes on to detail exactly what makes up a housing unit.
When a survey is carried out in lots of different countries, the definition has to be harmonized to make sure that 'household' means the same thing in all of the places where the survey is conducted. In America, where privacy and individualism are highly valued, it's easy to understand how you could explain a household as: the people who belong inside when the door is locked at night. But you can certainly see how household sizes could get ridiculously huge if you ask a question like 'who lives in this housing unit?' in a place where extended families live together on large compounds. As a result, in a lot of surveys in developing countries, the definition of a household has been stripped down to its essence: people who live together and eat from one pot.
I really like that way of defining a household. I think that's a poetic way of summarizing a potentially complicated web of relationships. The people who have the strongest social bonds are usually the people who eat together every day.