There are various “definitions” of icing +5,+3, visible moisture 1000m vis and so on. Snow isn’t icing necessarily. Your first stopping point is the flight manual for the aircraft you are flying and specifically the limitations section. Icing is very localised and can go from nothing to heavy and back again in a few moments. If you’re doing your IR you’ve got enough on your plate without worrying about icing. If your flight will take you IMC below about +3 deg C then it’s probably not worth bothering unless your aircraft has an icing clearance of some form