From the Overview: "The FAQs [frequently asked questions] for the signature verification and curing process are provided separate from the Inbound Ballot Process guide because this process is not performed or required in every state for accepting mail ballots, or absentee applications, for counting. On its face, the process is simple: Does the signature on the envelope match the signature on the voter registration form? Yes or no? When dealing with just a handful of returned mail ballots, this is a manageable process. When dealing with tens of thousands of signatures, this review has the potential to become a bottleneck in the process. Having a highly organized process and a well-trained team of verifiers is the key to success."
U.S. Election Assistance Commission: https://www.eac.gov/