This is the URL to which a user is redirected to, right after they log in, if...

1) Access to this product has expired,

AND

2) Setup > Config > Redirect Expired Users to Renewal Page Upon Login? has been set to "Y"

However, if the user has access to multiple products, and access to more than one of those products has expired, then they will be redirected to the equivalent global field at Setup > Config > Post-Expiration Renewal Redirect URL (Global) right after they log in.

WARNING: For any kind of renewal redirection to take effect upon log in, you must also set Setup > Config > Redirect Expired Users to Renewal Page Upon Login? to "Y"