IMO it's dodgy but I suspect it's all too common.
To get a neat job the sockets/switches need to be removed during the plastering so the plaster can go behind the sockets. The circuits would ideally be isolated during the work, but that is difficult in an occupied house. The accessories could be removed and bypassed with wagos, but you would still have the problem of how to cover the temporary splices. There exist specific shields to cover the sides but they are a relatively new thing, and I suspect also make it harder to get a good finish on the plastering.