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