Documents are not notarized. Signatures are notarized. Notarizing a signature on a document is an acknowledgement that the signature is, in fact, that of the person named in the document whose signature is required to execute the document. Notarizing a signature is usually required for any document that will be recorded on the public record. This is because the public recorder (usually the county recorder) will not record the document unless the signatures have been acknowledged (notarized).
If an operating agreement is to be recorded on the public record, it would have to be notarized. This would be rare because operating agreements are usually not required to be recorded. However, if one were required to be recorded for some reason, let’s say the parties to the operating agreement want it to be of public record, then the signatures on it would have to be acknowledged (notarized).
Documents that typically require recording are those that transfer interests in real property. Some loan documents require recording, like regulatory agreements for bond-financed developments that have received government subsidies. All of these, then, will carry acknowledged (notarized) signatures so they can be recorded on the public record.