It is especially important to destroy your old will where you have made changes to who inherits, or who you appoint as guardian or executor. An undestroyed original will, raises the obvious presumption that it was not revoked. If you have more than one undestroyed will, you run the risk not only that someone will deliberately probate a will which you intended to revoke, but the risk that they will do so accidentally, or even be forced into probating it.
The purpose of destroying an old will is to prevent someone else from attempting to probate it in Court. In addition to destroying the original and all copies which you may have of an old will, you should advise the attorney who drafted the old will that you have made a new one and requesting they destroy it. ( lawyers will request a letter and identification when providing the original will to you)
There have been multiple cases where someone contacted our office to see if we had a will, when informed of the date on the will they were sure that a newer will was made, but not being able to find it the old will was probated. If an undestroyed, original will is in existence, it is near impossible to persuade the Court that it was revoked.