I'm a notary and some of the answers given here are incorrect for the State of Ohio.
A notary isn't always "only" verifying information and having someone sign documents. A notary very often has to administer an oath or acknowledgement to the person signing the document which means the person signing has to know what they are signing and the ramifications of it.
Some documents have a notary clause that only states the person signing has represented themselves to be the person signing the document.
Some document have a notary clause that indicates who signed and that the person is acting on their own free will and is of sound mind to sign the document.
There are certain criteria a notary is supposed to ask in some instances to make sure they are comfortable that the person signing is competent to sign. The signor has to be aware of who they are, where they are and the date.
Our POA form here in Ohio requires an acknowledgement be administered to the signor. I don't notarize just knowing the person is who he says he is.
Just last week I was going to a hospital to obtain a signature on a POA and left without having her sign it because I was not able to determine she was aware of what the document was, who she was giving POA to, who she was, etc.