Turning off the a circuit 1 at a time method is the way that doesn't require any special tools.
It is 100% accurate once you find the breaker.
It takes 2 people or a lot of trips back and forth.
Doesn't work if there's a error with the circuit fed from 2 breakers.
That would take turning off every breaker then each circuit on 1 at a time.
Many cases this is not acceptable by the customers.
Remember working in a property when another EC was going panel board after panel board looking for lighting circuits, shutting off lighting on the operating casino floor, then back on. That lasted about 2 minuets before management jumped on them. Another example is slot machines, tons of circuits. They can take a bank out of service and rope them off to shut down and work on. But you can turn off every machine until you find the one. They would loose the players and be open to gaming board reprimand / fines. Anything with computers you take the chance of something not rebooting and data lost. From surveillance, desk tops, & IT rooms. Even at a residential home it causes the modem, router, and satellite to reboot. You think your done and the customer says the TVs don't work. Then you need to turn on every receiver in the house and let it restart for 10 minuets to show that it's fine.
Still it's better than the short circuit method. I am embarrassed to say I worked with people that did this.
Testers. The way to go. Not all are created the same. Some cost $20 others were over $1000. Don't know the price today. As said some work live, others dead, and some just don't seem to work. Really depends on a lot of factors how clear of a reading you get. An 10-4 MC cable a few hundred feet with a load on each leg can read on all 4 conductors.
Common since, investigating, and experience help. Look for any box or conductor labeling on the one your in or others associated with. Wire color. Number of conductors in cable or raceway if you found the home run. Type & size raceway / cable if you have the home run. Pull on the conductor if you have a raceway home run with someone looking on the other side. Direction from panel of home run. Was the home run ran above the ceiling, thru the wall, in the floor, below the floor. The schedule may have something related to the area your working on. Such as a home with a dishwasher circuit the other conductor in the HR may be a disposal or counter top rec. With commercial it could be labeled something that is no longer there such as a different business name. It helps if you could ask someone what was there (where your working) before or where was this (business not there) if the schedule seems inaccurate. Or a question was this always here. Many times someone will say no, this used to be this before they remodeled.