you should not use snow tires year round. They are made of a soft compound rubber that wears much faster than all-weather tires. Winter tires also don't handle nearly as well in dry conditions due to the special rubber compound that is designed to allow for traction in snow and icy conditions. If you have studded tires you certainly can not use them year round, and in some states you can not use them at all. In CT they have a law that states that snow tires can only be used during designated months where there is a possibility of ice on the roads. I believe its November - April.
Yes, with winter tires wider isn't better. The tires rely on their ability to pack the snow, then grip it to get traction. If too wide of a tire is used for the weight of the viehicle then the snow won't pack enough to allow for sufficent tration. Thats the reason most snow tires have a much lower speed rating than all-sason tires. A standard snow tire might have a speed rating of between 70 and 80 MPH, a performance winter tire will have a higher speed rating but not as high as a non-winter tire.
