Hi @KellyBetzold
The main reason I can think of for having multiple logins associated with an account is if you have multiple authentication providers, and the person has a different login name under each provider. For instance, we're part of a multi-campus university system, and folks have one set of login credentials issued by our campus. However, if they are also associated with another campus, we allow them to use a different login page and log in with credentials from the other campus, and that requires another login associated with their account.
Merging accounts will also result in the person having multiple logins, but you would want to decide whether there is any benefit (in your situation) in allowing them to keep multiple login names.