Chains are very important for traction when there is ice on the road. Nothing else equals the traction...nor the bother. Some states require chains on trucks in snowy mountains both on the drive wheels and on the last trailer axle for braking. Keeping the trailer behind the truck is a good thing. (And I've towed my travel trailer on icy mountain roads with chains on the braked trailer and on the truck with good, but slow, results.) Different states and different provinces have different laws. Washington requires all vehicles to carry chains in the mountains in winter. Sometimes approved traction tires are OK, otherwise chains must be used. Sometimes 4wd is OK with approved traction tires, otherwise chains are required. Sometimes chains are required for everybody. When traction tires are required for cars, chains are required for vehicles over 10,000# GVWR. Oregon is stricter than Washington. I like Wyoming's Basic Chain Law...if you slide off the road, you should'a used chains, and you deserve the citation you'll get. I've seen a time in the SF Bay area where the hail was so deep that only the CHP with their chains got through.
Never drive with chains over 25 to 30 mph. You'll shred the chains, and then the broken chains tear stuff apart on the car. Never drive far on snow-free pavement with chains. Always practice putting the chains on at home on a dry driveway in the daylight. When you need them will always be in the dark, in several inches of snow, in the cold and wind. Be sure you have a good flashlight, warm gloves, and dry tarp or something to lay on. Get the chains as tight as possible, move ahead a short ways and re-tighten.
Some 4wd owners prefer chains on the front. I don't. That would be OK in very slow driving, but up to speed centrifugal force pulls the chains away from the tire and they might hit something important--brakes or something. Also, I greatly prefer chains in the back for braking. Again, keeping the back end behind you is a good thing.