Opt-out results in a profile no longer being targeted by any delivery or by deliveries from a specific channel.
To give profiles the ability to opt in or opt out, you have to create a dedicated landing page. For more on this, refer to Setting up opt-in and opt-out landing pages.
Profiles can also be opted in or out manually by an operator. For more on this, refer to Managing opt-in and opt-out from a profile.
Opt-out profiles are automatically excluded during the delivery analysis in order to speed up deliveries (the error rate has a significant effect on delivery speed).
For more on services subscriptions, refer to this page.