The other two are to exhaust CO2, fumes and particulates, but I presume that the note about showering is for removing moisture from the interior air and prevent

The other two are to exhaust CO2, fumes and particulates, but I presume that the note about showering is for removing moisture from the interior air and preventing mold growth. Ideally you want external exhausting vent fans in every kitchen and bathroom, although lots of places have nothing at all or only internal vent fans.