Context for those who haven't worked in the field: A PLC is a programmable logic controller. They are typically programmed with ladder logic which grew out of discrete relay based control systems.
Generally they're controlling industrial equipment of some sort, and making changes without a thorough understanding of what's happening now and how your change will affect the equipment and process is frowned upon.
I interned briefly at a company which mainly built industrial control systems. One of its most interesting features (which is also very mind-bending if you're coming from any sort of typical programming ecosystem) is that every "rung" is evaluated in parallel. (As a physical relay-based control system would have back in the day.)
Generally they're controlling industrial equipment of some sort, and making changes without a thorough understanding of what's happening now and how your change will affect the equipment and process is frowned upon.
https://en.wikipedia.org/wiki/Ladder_logic