To whom?
Advice cannot substantiate anything, this is the job of evidence.
There is certainly no implication at all that adding an unsubscribe link will tend to identify your message as not spam.
Benefits of unsubscribe links:
As the mailer, you may be easily notified that a recipient no longer wishes to receive mail from you. Recipients will more likely have a more positive view of you if you provide one along with a brief sort of apology in advance.
As a recipient, this allows you to unsubscribe easily. Self explanatory.
As a spammer, including an unsubscribe link is an exercise in social engineering. Recipients clicking that link let you know you have found a valid email address.
