Even more so, if it’s just there you’re making it easy for the customer to find someone bidding less to execute new projects. Guess who they’re calling if they don’t have the plc project (or don’t understand they need it). Job security.

Plus, yea, someone could really make a mess even if they have the best intention. A guy from my company almost uploaded the wrong program to a large bioreactor. At best it would have made the bioreactor just unusable until corrected. At worst it could have broken the equipment or caused a safety issue. This guy had been around the block a few times too. Luckily someone noticed before it was too late.

I don't get into PLCs, per se, but I've done some stuff with other building-scale gear.

Like: We took care of the centralized controls for the inmate portion of a jail that was built in the 1980s. All the wiring for all of the individual doors and intercoms was documented in one old 3-ring binder. (There were probably 3 copies originally -- for the architect, the maintenance room, and the equipment room, but 1 remained.)

We rejiggered the controls for that whole jail back around 2010 or so with new kit and had been taking care of it since then.

One day, around 2020-ish, they called us because the book was missing. I didn't have it (I never once left the equipment room with it), and the co-workers who had been there insisted that they didn't have it either.

We'd get occasional phone calls of "Hey, we really could use the book for our building back if you guys ever find it." They weren't angry calls, but sheesh: That book had real value and getting stuff done without it was difficult. So every time when they'd call again, I'd ask around our shop -- again -- if it had turned up anywhere.

And then, finally: One of our guys cleaned out his truck and found it. He must have taken the book out to look at and have a smoke about some problem or other, and then it just stayed in his truck. For years.

This shit happens. People are imperfect and sometimes we screw stuff up.