They are mainly for slick ice and snow. I carry a set of real chains (steel) for when it gets nasty out. I've had to use them a few times during a freezing rain storm last winter where all emergency vehicles were required to chain up and general travel wasn't advised for the community.
I Have all season, all terrain tires fir year round use in Fairbanks; but since relocating to the Anchorage bowl; there's enough of a difference in the weather that I wanted different tires. Fairbanks ice gets hard and its like driving on summer asphalt. Anchorage ice hovers around the freezing point and gets slicker than snot on a door knob.
Now I have a spare set of rims permitting faster tire changes each season.