OAuth2: Why do we need redirect URI for user agent

Question

I recently made a small app with webserver flow. Now I am trying a user-agent example. I am wondering why do we need to define a redirect-Uri in user-agent flow.

I am working with Saleforce.com API:

http://wiki.developerforce.com/page/Digging_Deeper_into_OAuth_2.0_on_Force.com

redirect_uri The authorization server will respond with a redirect to this URI. This parameter must match your application's configured callback URL.

Answer 1

Talking about the user agent flow, redirect-URI is the perfect location which the user gets redirected to after they click Approve on the approval page. Added onto the redirect_uri is a hash fragment.