In computer labs (one of which is physically open to anybody to walk into 24/7; the rest have more limited hours but no real physical access control during hours of operation), everything is locked down that reasonably can be and there are cameras. Usually it's one long cable running through each computer and monitor per row.
In offices, we generally only lock laptops, and not everybody is consistent about that. Monitors and desktops are bulky and less valuable; laptops tend to be expensive, easy to carry and not suspicious to be seen carrying.
We're a university and there is no access control to our hallways during business hours. There have been cases of laptops "walking off" out of offices during business hours. And cases of vaguely suspicious people walking into offices and acting lost. (which could be a genuinely lost person, or somebody trying office doors until they find an empty office with something valuable)
The cables aren't much of a deterrent. I'll bet a determined thief could get through one with nail clippers in a matter of minutes (or a bic pen in seconds?), and a thief can always just grab the laptop and yank hard, but that leaves visible damage on the case (making it more obvious it's a stolen laptop being sold, but not really decreasing the value).
Personally I always lock my door, but many wouldn't to go 20 feet down the hallway to a printer, even though it leaves plenty of time for somebody to walk off with a laptop. Cable lock increases the time above 1 second, which is a big help.