I shut things off because it's faster.
I change 347v ballast all the time live, and every so often I tie into a 600v splitter without shutting it off. I work, pull in/through 600v switchgear all the time, but keep a safe distance from the busses, Ill bolt in 600v switches/breakers to a live bus.
Im very careful, there's no room to slip, even if I did I would be sure that there would be no I'll effects, if I'm that close I shut it off or find another way.
I really dislike working in 347/600v live junction boxes, especially troubleshooting since in that case it's not my work , since I wouldn't be troubleshooting my own work.
With all that being said, my guys don't work live. Ever. I did recently change the panel in my residence live. My father in law who is also an electrician had his best friend killed from a shock while working in a confined space - **** is real.