I wouldn't think having a small run is much different than a kennel or cage.
I'm one that would not want a 'cage-free' shop for my dogs to go to, nor would I want to work that way. Where I'm at now, our own dogs sometimes are loose, there's one that is almost always loose, but he was raised in a shop and 'knows' how to act, stay out of the way, etc. Only a few client dogs are allowed to roam, and those are only ones we have known for years and can trust to behave.
Not only do you have to worry about dog-on-dog interactions, but also you'd want to dog-proof everything, including cords. If they don't chew on one, they can walk into one and pull your equipment off a table, or yank the plug out of the wall. Then you also have to worry about door-charging dogs that try to escape past your feet the instant the dog is cracked. Trying to grab a dog on the floor can be extremely difficult vs working with a dog in a kennel.
If it's a completely separate room, for each separate dog, it seems a huge waste of space to me. Unless each "cubby/room" is so small you might as well just use kennels.
Just my $0.02