Your experience with utility accuracy?
What are your experience with utility mapping accuracy?
My experience is that I've seen the full spectrum of accuracies.
From accurate to 0.1' all the way to unreliable under 40'+ and worse yet - out of date as to existing or not.
That's why you need to include metadata with the mapping - there's nothing wrong with data that's only good to the nearest 40' as long as you understand that limitation so that you can decide whether it's appropriate for your use. When you do use other folks data - you need to include that metadata so that all end-users understand the limitations (accuracy, age, source, etc.)
I think you will need to flesh out your question a little more in order to generate a worthwhile discussion.
I have found that when gas-lines were hit in the course of construction that the accuracy was very low, on the other hand many times I have seen directional boring hit on the money when the utility mapping accuracy was sufficient.
Are you asking about mapping or locating? Conventional methods or something newfangled?
In my rural element, was taught within a foot.
Usually, I attempt to locate to "the center of" pole, valve box, water meter box, gas pipe riser at meter, pipeline vent, middle wire transmission line, and so on in relation to the location of boundaries.
Usually, the utilities have changed location every time I go back to do a new boundary.
The electrical utility engineers I work with use mapping grade field equipment for their records software. Their recorded data is lat/long. The comparisons I've run into when working on some good hard locations are anywhere between 1' and 15'. I Don't know the story but there are a few older files that start approaching 100'. I guess there was a learning curve when they implemented the system. The engineers blame the CAD techs. I've never asked them, but I'd bet the CAD techs blame the engineers.
It's not difficult to work around though. When I get a pole location on a work order in lat/long it's not hard at all to determine which pole it is.