The traditional Benediction, also known as the Aaronic Benediction, comes from Num. 6:24-26. More than just nice words to send us on our way, the Benediction actually gives us something: the LORD is placed on us (Num. 6:27). Just as the name of the triune God marks us in the Invocation at the beginning of the service, so is that name given to us at the conclusion. With the name of God comes all the gifts that he desires to give: blessings, protection, grace, and peace.
When another benediction is substituted, great care should be taken so that the words are indeed words of blessing, words that convey the Lord's gifts to his people.