ZANE SAID:
"Because that token is your key to their information, their profile, their demographics; everything you need to keep up with your incoming traffic without the hassle of storing it yourself."
OK, but that case is when you make 3rd part applications available in your site, not when you use only user credentials.
I am asking what is the advantage of using "user credentials" instead of $_SESSION.
The user credentials receive a Username and Password, then return a token in json. Then, you have to send the token back to the server to continue to be "recognized", and what is the diference of sending him a SESSION_ID?