Today most sites ask their visitors for some personal information. Their purpose for knowing more about you differs from site to site. Some sites require your information to send you prizes, enter contests etc. So we find various uses for collection of personal information. But before you give out information about yourself, look for their privacy policy and carefully it.
Privacy policies are easy to locate.
As a child, make sure your parents know about any personal information you are giving out while filling out forms. Take their permission always. Its safer that way. So read them with your parents before parting with your personal information. This in a nutshell is what privacy policy is all about.