I agree with al the previous comments. Let me add this. To get the full benifits of Awd, you SHOULD use winter tires on ALL FOUR WHEELS. A competent tire store will not even mount two winter tires only which is unsafe and could damage your drive train ! Newer winter tires do quite well on ice, even without studs. If you live on a dirt road that is frozen all winter and there are lots of hills, studs are helpful. Anther wise, not necessary IMO. The problem you will have with Subarus may be finding cheaper steel wheels to pre mount the winter tires.
The Outback is very difficulty to do. Hopefully, the Impreza is different. It is much cheaper in the long run to deal with snows in this way rather then re mount them every year. Plus, you can run your summer tires or all seasons down to the wear bars and not worry about lost winter traction. This results in a net savings over the life of the car as opposed to just one set of tires. It’s no brainer.
Awd cars can be SAFER in snow with snow tires then without compared to 2 wd cars. You may need them more for awd then when driving a fwd car. This may seen silly to say, but snow tires are needed more for turning and stopping on Awd cars, and not so much for acceleration which Awd cars can do adaquatly without in most situations. A fwd without snow tires will have difficulty accelerating, often keeping your speeds slower. Get’m ! Think of it this way. You would not put poor performance tires for cornering on a Corvette and them try to drive it up to it’s capabilities.
The only place I might disagree with most is, that i feel nearly all winter tires are quite good in winter traction. You can find moderately priced winter tires that will work instead of the most expensive if you can accept some of their compromises, especially if you travel in the city mostly. For example; General Alumax 's are a very good, moderately priced snow tire that scores well enough on Tire Rack tests to be considered as much as more expensive ores that may only perform slightly better.