One way that a number of contract disputes in California actually start is when someone who feels they are getting the worse side of a deal say that they did not sign the agreement. Once a person states that they did not actually sign when they did, a large and expensive legal battle may ensue. However, by having a notary witness signatures to the contract, this is no longer the case.
The point of having notaries present during signing is that they not only view individuals signing a document or contract, they also verify that the person is who they say they are, usually through some form of acceptable photo indentification. Notaries are required by state law to keep a log of all signatures that they witness as well as stamping the document. The benefit of using a notary is that a number of state courts and all federal courts have decreed that a notarized signature is automatically considered authentic.