If the communication was sent in error, your unsubscribe information will be sufficient. Without it, you sacrifice quality and risk ticking off your customers. You must be sure your customers agree to let you share their information with others. DO include unsubscribe information in every communication you send. One or two extra steps to the opt-out procedure are acceptable.
Folks get grumpy when they opt-in to something and never get value for having done it.
And they get really grumpy when they opt-out, but keep getting your mailings. Either way, you are abusing your customers, and they aren't going to take it kindly. DO these things effectively and in good faith and you'll have your customers feeling happy about having opted-in. DON'T manage your Permission Marketing scrupulously, and you can kiss not only your existing customers, but also your potential customers goodbye. They'll appreciate it.