Surveys (questionnaires and such) are a major part of research in the social sciences. They come with their advantages and disadvantages.
The major advantage of doing a survey is that you can gather information on a variety of issues from a variety of people. For example, you can gather information about how people spend their money. Or about how much time they spend with their children. Or about how happy they are. You can ask about just about any topic you can imagine.
The major disadvantages of surveys include:
- People don't have to tell you the truth. They may tell you what they think makes them look good (like that they spend more time with their kids than they really do).
- People have to self-report what they do and they might be wrong. If you ask how much people spend on some particular kind of product, they might not remember or they might not really know. So instead they just have to guess and your data end up not really conforming to reality.