I have started on the task of labeling all my breakers but in this process it has left me with one major issue, I have one breaker that doesn't kill anything in the house. During the checks every other outlet, ceiling fixtures, appliances are accounted for, but I still have a single 15 amp breaker that I can't figure out what it controls. Is there any advice on figuring out where this breaker goes to?
Note: This may seem silly, as it's just the opposite of what you've already done, but I promise it is not in jest.
Try turning off ALL breakers except for the mystery breaker. It is completely possible that one or more circuits were erroneously "double fed" by this breaker and another.
Alternatively, you could have something not-so-obvious like an exterior light, garage door opener, doorbell that is powered off this circuit.
Lastly, someone could have "dead ended" an unused circuit by simply capping it off where it terminates, but leave the breaker and wiring for future use.