Google Gmail Weird Way of Handling Contacts

From Gmail's help center,

"Email addresses are automatically added to your Contacts list each time you use the Reply, Reply to all, or Forward functions to send messages to addresses not previously stored in your Contacts list."

Is this a pro or a con? I see this as a con. Having unknown in my contacts certainly does not help me. I hope Google will be around reading blogs.

http://googlesystem.blogspot.com/2007/12/who-are-my-gmail-contacts.html