A question regarding the Session Class

[eluser]EEssam[/eluser]
Hello,

I do not understand what is so good in having the following information available:

[array]
(
'session_id' => random hash,
'ip_address' => 'string - user IP address',
'user_agent' => 'string - user agent data',
'last_activity' => timestamp
)

How can this help me in creating a member area, for example?

Please clarify. Thanks.