in addition
1 You could get into a situation where the slats could not be retracted due to build up or asymmetric slat if only one retracted
2 You should always be thinking about leaving icing conditions rather than sitting in them. Severe icing of which no a/c is certified for continuous flight in, can be caused by exposure time. EG climbing through a layer of icing may present light icing but continued exposure at the same level may cause severe icing build up