Adding a Digital Signature to your signed document is a really good idea. In fact all documents signed via Signature Request or In Person are always digitally signed by CrunchSign. It is only optional when your are just signing a document yourself.
Digital Signatures encrypt the date, time, IP address and identity of the Signer inside the actual signed document.
It also creates a checksum of the signed document's contents.
What does all this mean?
It means that the document content can be verified (either in CrunchSign or Adobe Reader) at a later date. You can check that the content is the same as when the Signer(s) actually signed the document. This is useful for both sides of any agreement/contract signed...
It also means that the time, location and identity of the signer(s) can be verified - to avoid any disputes.
Forging a Digital Signature is next to impossible, and actually provides a much more secure, tamper proof and verifiable signature than traditional 'pen and paper' signatures.