We are still allowed to have basement floor drains connected to the city sewer. On a septic system I can see that it would be good for them not to be, although they do provide a visual reference to the functionality of the sewer drain. A hack that is frowned upon is to knock a hole in the side of a basement KC drain to let ground water under the slab escape into the sewer. Our town has an ongoing smoke test program to help find violators, of which there are plenty.
Lee has reminded me of the reality of a city sewer turning into a high pressure fountain. It can happen in big rain events or blockages if your basement is lower than the nearest sewer man hole cover. DAMHIK. The smoke testing and installation of back flow preventers is an on going neighborhood saga for us.