The practical criteria seem to be related to whether or not there is additional foot traffic, pressure on parking, security issues and impacts on common property.
A resident who used the common property pool for children’s swimming classes is one recent example that springs to mind. Another was a tenant who purported to offer a massage service when it was in fact a brothel.
Peter is right about home offices (I’m sitting in mine right now). But I have most of my meetings in nearby cafes. If I had people trooping in and out all day, I suspect I’d be getting a tap on the shoulder from the building manager threatening a “change of use” complaint to the local council.