CGI

I have a question to which I am trying to find an answer. If suexec is enabled in apache, a user can run his scripts under his own ID. It is fine. My questions are

1. In the first place for what purposes a user want to run CGI under his own ID.

2. Whatever is the purpose , why can't we change the permissions for the user accordingly in his virtual host entry in httpd conf file

3. Also I read that there are dangers in enabling suexec. What are the dangers. Some where it is written that when other users can execute his CGI scripts . it poses a danger to the server. How is this caused. Please explain me with a scenario.

I have read many articles , but I could not understand why the users want to run CGI scripts under their own ID. Why can't they be run under server's ID as nobody .

Thank You very much.