Like other emergency preps, mostly you don't need chains, but sometimes you do.

Both our vehicles are AWD and the first priority is good tires. Both wear Bridgestone Dueler Revo AT2 tires. These are soft, sticky, dual compound tires which get really good traction in the wet (Pacific NW) and do good in the snow.

Then, I have sets of chains for the front AND back if the tires and AWD combined need help.

Personally I break chains down into cable chains, diamond chains and chain-chains.

The former two are good on packed snow and ice and OK for higher speeds. The latter for deep stuff. The former stay tighter to the tire.

In the past, I had both diamond and chains for our Jeep WJ, although now only the latter for our WK2.

WRT dedicated snows, I feel they are viable replacements for packed snow and ice, but not for deep stuff. Also, my understanding is tires have a shelf life, so even if yours snows haven't worn out, they may harden and lose their effectiveness in a few years.

-john

Manual chains are the way to go. Simple and easy to fix if ever needed. We have a full size 4wd truck and carry a set of heavy chains from October to April. As the truck has 20" tires, there was a lot of sticker shock when I purchased the chains.

As we sometimes pull a friends enclosed snowmobile trailer in winter, the trailer also has a set of chains. Learned the hard way a few years ago while slowly descending down a mountain pass. Even though the trailer has electric brakes, it jackknifed around and just about pulled us off the road.

Also this year, .gov is enforcing over almost all mountain pass roads, the minimum acceptable tire rating is M&S or those tires with the snowflake designation.

Hopefully this enforcement helps to keep the mountain pass roads open more, as many times the roads get closed due to cars and commercial trucks as they do not have the proper tires and or chains.

Discovery Channel Canada has very good series that depicts a heavy rescue towing company and it employees who attend to many snow related highway closures and vehicle recoveries in British Columbia and Alberta Canada.
Highway Thru Hell

+1 on HtH -a very interesting show