Surveys are important and surveys are useful if they are made with perfection and carried out in an effective manner.
The purpose of conducting surveys might be different as it depends on the nature of survey and varies from survey to survey.
Surveys help the researcher to grasp all the required information and data that they are seeking in order to complete their research.
For example, before elections, many surveys are conducted to determine who is leading and popular for the people. The result of survey is useful to those people who want to know who is the leading candidate even before the election. It becomes possible to know the ranking of candidates based on survey without waiting for the election day to come. After all, the purpose of survey is just to give information that is reliable and representative that people can trust with.
Most surveys are used on sites to lock you out on files you want/need and are completely bogus. Most of them force you to give up your credit card information, and watch your money go down the drain.
Besides, why even do them, all you do is give your opinion on something. It's not like it's going to do something
Unless it's quick and seems like something that is at least mildly interesting I turn down surveys. I imagine many others do the same. Furthermore if I am taking a survey over the phone and people are in the same room as me then I don't always give honest responses.