Taking out your winter jacket from storage and discovering that you forgot to wash it before putting it away is not so fun.
It's just as boring to find your patio or deck dirty and stained when spring comes. By cleaning and tidying between seasons, it becomes both easier and more enjoyable.
Scrubbing away the year's stains from barbecuing, juice and coffee from the patio makes spring more pleasant. If you are a grower, it is a good idea to clean pots and tools as well, despite the cold, pests can actually overwinter and give a bad start to the next season. By soap-scrubbing your tools, you avoid this.