Statistics are almost always abused. If you have the slightest worries about the intentions behind those questions, simply don't participate. Most of them are used for marketing purposes even if they tell you something else. Hint: Usually 90% of the questions are just red herrings and the answers for those will simply be discarded. The real topic is more or less hidden behind a few of the questions.

"Interviews" on the phone are even worse. Either they actually want to sell something or they want to get information from you using social engineering. Keep in mind that it's your time and their money. If the survey is used for marketing purposes, you will have to pay for the study it in the end even - assuming you buy some the products it's used for!

Such firms should better invest in quality of their products and better customer service instead of wasting the time of people. Don't let them use you.

Further keep in mind that surveys are also done in order to justify a opinion. They'll just interpret the collected data in any way they want and then claim "Hey, it's scientific and objective!" when in fact it's usually just a very a single narrow interpretation of the results.

Often online surveys troll you with a point system like "you get 5 points per answer and for 100 points you get a free [whatever]". Don't fall for that. First of all, they might just want your email address in order to spam you or to sell to it. I'm not kidding at all. Even if they're really interested in the survey, it's pretty unlikely that you'll ever reach enough points to get the promised bonus thingy. And then, even if they are honest about that and you one, it'll hardly be worth your time. Just consider the simplest non-annoying job you've ever done and compare the income with that.