Direct Linking Vs Landing Page

I want to know when to use Direct Linking and when to use Landing page in terms of promoting single page offer or double opt-in. Because I read so many tutorials says that direct linking is good for email/zip submit offers and surveys. So I want to know your opinion.
Thanks

For me I use direct linking once I already have the user on a mailing list, part of a group or anything where I know that person is a qualfied lead i.e has bought or used services before or has joined to a mailing list.

Landing pages I use when trying to capture a sale, user data or promote a service via a paid advert both online and online to a targeted market pool where I have no idea how the audiance will react to the promotion or business.

In other words I use direct for established user base and landing to capture a new user.