"By Whom Affidavit Is Made" wants the name of the person signing an oath that the bride and/or groom is 'qualified' to marry. If either of them is underage, the signer of the affidavit is giving permission for them to marry. The signer of the affidavit might be saying one or both of the parties has legal residence in the county issuing the license. The affidavit is an oath that legal requirements to marry are met and the person signing it is usually a parent, a family member, or a person who knows the couple well enough to know there are no legal reasons why the couple cannot marry.
The signer of the affidavit IS NOT the county clerk. We do not need the county clerk's name on any of the indexes but if parents had to sign for underage children to marry, or a neighbor has to sign saying he/she knows the individual lives in this county, a researcher wants the name of that person signing the affidavit. It could be the clue needed to take the research back one more generation.
Thanks for all your help and thanks for paying attention to details like the above to 'get it right' for future researchers!