Sometimes breakers are installed in panels but are not wired, they actually just take up space where a knockout has been removed so that there can be no accidental intrusions to an area where there is a live bus.

Leave them off, if they were in use you will eventually find where.

Could be either. Maybe they don't even have a wire on them, or maybe you're just not finding what they control.

Hopefully you wont "eventually" find out they feed a sump or septic pumps, the smoke alarms, or some other important but less obvious outlet.

Hopefully he would check critical circuits after shutting them off, which I considered mentioning but figured it was common sense. How far do you go with advice without writing a novel? If people want to DIY on their home systems they bear at least some responsibility to use common sense.

This post was edited by joefixit2 on Sat, Jun 21, 14 at 12:20

And this he knows it's connected to something critical how?
When the basement starts flooding? When the toilets start overflowing (in a fit of stupidity, both the pumps and the high level alarm, nick named the deep sh*t alarm, in my old house are connected to the same breaker).

"And this he knows it's connected to something critical how?"

by turning off the breakers and checking to see if the critical stuff still works?