I have a mini ex and a TLB so I do my own.. when I was working with a crew on some larger projects, the boss rented equipment and there always were several guys proficient at running a machine. That said, one job (utility scale solar) the company we were working for provided a guy and machine. That guy wasn't the sharpest tool in the shed, couldn't/wouldn't read the blueprints to get the layouts, but he dug the most beautiful trenches I have ever seen. They were a joy to work with. He would ask me a couple times "how's the depth?" And I would check and it was always like no more that +/- half an inch.