The USCIS Adjudicator’s Field Manual (AFM) is a dynamic document that is used by the USCIS to disseminate policies and procedures to the vast amount of adjudicators involved with administering immigration benefits. There is a Redacted Public Version available for all to read. The function of the public AFM will eventually be replaced by the USCIS Policy Manual.
The Adjudicator's Field Manual is the best place to go if you are interested in the minutia of a specific procedure that USCIS employees undertake. In terms of its usefulness to the public, it's mainly an exercise in transparency to see the policies, rules and procedures each USCIS officer is expected to operate under.