Massachusetts Attorney Thomas Swain Smith explains the benefit of attaching a Self-Proving Affidavit to your Last Will and Testament:
A self-proving affidavit is a sworn statement attached to a Last Will and Testament, signed by the person creating the Will and the witnesses, that attests to the validity of the Will.
It is not a necessary component of a valid Will but can save a lot of hassle when the will needs to be admitted to probate.
During probate, the personal representative of a will must "prove" its validity to the probate court. Doing so involves convincing the court that the document really is the last will and testament of the person it appears to be.
A self-proving affidavit is equivalent to the sworn testimony of one of the witnesses and it proves the Last Will and Testament on its own, eliminating the need for finding the witnesses years later and bringing them in to court.http://www.masslawonline.com