In this day and age, we need to make sure that we are all protected from those unscrupulous business folks who will try to cheat us out of what we deserve. This is where a notary comes in handy. A notary can protect you from fraud. I once won a contest for a free copy of software. In order to claim my prize, I had to sign a document and have it notarized. The contest folks wanted to make sure that the correct person got the software and that I was who I said I was. Not just anyone could get the prize because I had to "prove" who I was.
That proof protects against fraud. Fraud is defined as deceit or trickery, a breach of confidence in order to profit or gain an advantage. When I was claiming my prize, I proved who I said I was by presenting my currently valid, government-issued ID: my drivers license. Another such document is a state-issued ID or a passport. What I signed was an acknowledgement which stated that I proved who I was and it was I who signed the document. An acknowledgement is "acknowledging" that my signature on the document was mine and that I signed the document of my own free will. The validity of the statements in the document were not questioned. An Acknowledgement does not verify a document, just the signature on the document.
If I were to have sworn to the validity of what is said in the document, than I would have required a different form or notarization from the notary. I would have needed a Jurat. A Jurat states that I have sworn or affirmed that the statements in the document are true. An oath must be taken before the Jurat is signed and the oath is administered by the notary. A document needing a Jurat CANNOT be signed before going to the notary public nor before the oath is taken.
The Notary Public can provide an Acknowledgement or a Jurat but CANNOT choose which one to provide. That must be done by the client. A notary can describe the differences, but it is up to the client. Advising which one is needed is considered giving legal advice, and in California, a Notary Public cannot give legal advice unless they are also an attorney.
Your local or mobile notary can be of great help when you must make sure documents are signed by the correct person. If you run a business, there WILL come a time when you need to require a client sign something and have it notarized. That process protects you (the document creator) as well as the client (the document signer) against possible fraud.