Question: I am concerned about giving my EMail address to anyone and being flooded with spam. Why do I have to give you my EMail address?
Answer: We use your eMail address to provides a unique identification for each user. We also use it to send you your password so that you can access our system. If you participate in a survey where you need to log in then you will need to eMail your password to yourself and log in before you can participate.
Your eMail address is easier for most people to remember than a user name.
If you are creating a survey and asking people to participate then they will want some reassurance that you are how you say you are. While not perfect, your eMail address and the other information that you provide can give your survey participants some assurance that you are who you say you are.