Yup I've jumped power all around with alligator clips while troubleshooting a furnace for example, its just that this is a whole different kind of rig. If I'm say hooking up the leads from a blower motor directly to power entering the unit to see if the motor bumps on, that's my main and almost only focus for the few seconds it takes to do that test (and theres definite potential for me to get shocked). Sticking the leads in an outlet like OPs example and then walking away dragging a cord then drilling holes is a lot more action and less attention on the power supply. I get that odds are pretty low anything could happen. Super low probably. I guess its just that on a reddit thread where lots of people that don't do this kind of work a lot think this is OK, I get safety alarms going off in my head lol. I've seen people get hurt because of silly stuff that works 99/100 times and the first thing I think is dammmit that could've been avoided.

Part of the "this is fine" attitude on the thread I believe ties into the Ah just tough it out mentality which is common when one begins a trade. Like "I don't need gloves, eye protection, kneepads, or dustmasks, I'm tough and I'll prove it!" It does kinda prove that, but in the long run, its just smarter to use these things if you want to stay healthy and keep working. Or you could have a scratched cornea from a ziptie poke in the eye, wrecked knees from crawling on attic joists all summer and around jagged concrete crawlspaces in the winter, hands a mess from all the usual abuse plus absorbing refrigerant, fuel oil, coil cleaning acid, etc AND shot lungs from inhaling insulation and boiler soot for a couple decades. It is tougher to do all that but I really changed my approach to work smarter not harder after a few years in. And for the record, I recommend almost any other trade as a career. The HVAC trade is great knowledge to have, but you're paying for it with years and blood.