Do I have a use of session when user havne't login yet

[Mgccl]

I have read about session, and for now I found my session is just for personalization for users, here are the code.

session_start()
$_SESSION['username'] = $username;
$_SESSION['premisson'] = $permisson;
$_SESSION['language'] = $language;

I got 2 questions:
1. Should I genorate a session for every guest if there might need some temponary storage of some data?
2. To make a site secure, should I only allow session to genorate in the login page and no where else?

[Houdini]

Use session where and when you need variables to be accessed or assigned within the ectire time that a user might spend on the script. I am not really sure what it is you are wanting to do but using session_start() at the beginning of all the script you write while not necessarily efficient could save you when assigning or needing to acces on is necessary.