There are situations when it is useful to know the "observation type" of an exposure object. This is often pulled from a FITS header OBSTYPE keyword (e.g., object, dome flat.)
This ticket is to add "type" information to visitInfo to at minimum indicate whether the exposure is a science product or a calibration product. Ideally it would be more specific with classifications such as bias, flat, science, etc. I could see it being reasonable to have an assigned type label be either static or changeable depending on the use case.