There is no right answer here. Covering a unit in the winter will keep it looking nicer longer. However, an ac unit is made to be outside in the weather so it can withstand the winters. Covering the outdoor unit also traps in moisture which may rust out electrical components. Covering the unit also makes it a great place for mice to live in the winter and mice love to chew wires. We get multiple calls each year for mouse damage and a large percentage of them have to do with the unit being covered. It really doesn’t matter what you decide to do but there are more chances of problems if you cover it.