I've been there. I shut down a bunch of what looked like idle instances doing nothing to reduce spend. 80% of which were, in fact, doing nothing. I did drop off two vms that were supporting critical infrastructure.

Everyone who had done any work on them was long gone. I had done my due diligence to identify what they could possibly be.

Still, the day of reckoning came, and we got calls of services down a week after I turned them off. I spun them back up, and they were going again without any real impact to the business.

This turned out to be a blessing as the very next week the cert these same services depended on expired and if I hadn't learned about the system by turning them off we never would have known which boxes held up those services.

Also a lesson in what happens when people leave without any documentation on where the work they did lives and how it works.