Have done this too (and am not a professional electrician either) --- you use insulated tools and make sure you stay out of the way of any possible current paths.
Why not just shut off the breaker though? What’s the harm in that?
For effect. You want the client to feel that they got their money's worth and it wasn't something they could have done themselves.
Live feedback without additional expensive and buggy test tools. May be marginal, but if you are trying to guarantee a certain income/payrate, it’s easy to take shortcuts in a system you’re comfortable in.
Other devices on the same circuit that I didn't want to disturb.
Like what? A deep freeze? Genuinely curious. If this were commercial it would make more sense.
The light in the room where you’re changing out a wall switch.
How do you know it’s installed right without putting power through the thing? You’re going to turn the breaker off an on for every single switch? NOPE!
Flipping the breaker for each circuit as you start and finish working on it sounds eminently reasonable
It’s definitely what I would do, but I can see the disadvantage if your goal is to get in and out quickly and the switch is on the second floor and the breaker is in the basement.