In a world where garages are converted to Air BnB units, its important to understand that your property may not be able to be financed if it has an illegal use. Illegal ADU's are becoming more common, and these make financing very difficult. Before you make your basement a "mother-in-law-suite," consult your local zoning office, and the following video.
There was a time when banks thought that all you needed to do was remove the stove from the ADU and that would cure the issue (everyone knowing that the stove would be back in 30 minutes later). However, FNMA has made it clear that this is not the case and has never been the case. Instead, the ADU has to be effectively rendered obsolete as a dwelling unit with the stove removed, cabinets installed over the area. In other words, you can have a "man-cave/she-shed" but not an illegal ADU if you want any form of government financing.