In summer, plus sizing allows you to use a larger diameter wheel with a lower tire side wall, allowing you to maintain the overall tire diameter. This results in a stiffer ride and a wider contact patch, improving the look and overall handling by making the cornering/steering response better.
In winter, minus sizing is the best way to lower the cost of seasonal changeovers and achieve optimal cold-weather performance. Smaller-diameter wheels with narrower and taller tire side walls will help cut through the deep snow and improve traction on icy surfaces. It will also save you a considerable amount on the cost as you’ll no longer have to remove your tires from their rims or rebalance twice a year.