The pros and cons of running dedicated summer and winter sets of wheels/tires will depend on individual situations. For what it's worth, I advocate having dedicated summer and winter tires available if the different seasons of your area makes sense to do so. The alternative would be to run all-season tires year round, which I don't recommend, but opinions on that differ from person to person (a rally school I took a winter driving class at continually referred to them as no-season tires since there are no seasons where they are optimal in traction). My experience with running separate winter and summer sets is from the perspective of a (former) New England resident.
Benefits of a dual set-up:
- Having dedicated summer and winter tires means you maximize your traction during the different seasons. No need to compromise on traction and conditions with all-season tires. This is easily the most important factor.
- Allows you to use the wheels you favor during the summer where the conditions are less harsh.
- Wheel and tire fitments that better target winter conditions. Typically, narrowing your winter tires will improve traction. Going with a smaller diameter wheel and increasing the sidewall of your tire will also improve ride quality as your tire is now a larger cushion from pothole-filled roads and the extra sidewall height provides more protection to the rim from pothole strikes that you may inadvertently hit. Most who go with a smaller/narrower wheel usually just step down 1 inch in diameter and 10mm in width. Just make sure that going with smaller diameter wheels will still clear your brakes!
- Both sets of tires will last longer since tread wear is split across both sets.
- Winter traction on the winter tires will last for more miles than all-season tires, which must compromise on winter traction to also allow for decent wet/dry traction.
Drawbacks of a dual set-up:
- Up-front price.* You need to buy a second set of rims and a second set of tires for the conditions you are targeting (presumably, that would be winter tires). You'll also need a jack** to lift the car so you can swap the wheels, or pay someone to do it for you. This tends to be the primary reason people often stick with running just all-season tires year round.
- Storage. You need to store the wheel set you aren't currently using.
- Indecision on matching the tires and conditions. Summer and winter tires have recommended operating ranges for temperatures and conditions. Particular seasonal conditions can put you in a tough spot on which set you should use. What do you do if it's been 50 degrees and sunny and then the forecast calls for 3 days of low 30's and a little snow? At what point in the year do you decide to make the change?
- Traveling from a location with ideal conditions to another location with potentially inclement weather. For example, if you live in an area that generally sees nice weather and you wish to travel into some mountains where snow is likely, which set do you utilize?
Now, it should be noted some of the cons can be mitigated simply through experience, so the impact of some of them can range from fairly minor to non-existent. Again, that depends on your situation and your location/climate.
*It is up-front because once you've purchased the wheels, they should last until you decide you don't need them anymore. Purchasing the winter tires will, eventually, even out long-term since you are now splitting tire wear across two different sets of tires over the course of a year.
**I do not recommend using the emergency jack. It is not intended to be used regularly. Getting a proper floor jack with a lift capacity that comfortably covers your needs is highly recommended. For example, I tend to lift the entire front or entire rear of my Subaru Legacy at one time, so my jack's capacity covers more than 50% of my car's total weight.