I have learned to ignore these offers because in most instances they are used as ploy to get you involved in a program which you would not have considered to join into. Some of the seemingly legitmate ones may require too much of you to be able to be eligible for the reward which makes it not woth the effort.
I used it back in the day and since i was using a certain website that has those offers everyday i said why not, but i barely won anything.
I hate things like this and wonder what kind of people sign up for them as they bring endless cold callers and email spam. I only did it once and started to get texts which were charging me. I only realised when I saw the size of my phone bill. I had to contact my network provider to delete them for me. I learned by that but there must be people who do them as reward sites are full of these kind of offers.