If you lock the front it should be a locker that you can unlock when not needed. Because like the others said, all locked at the same time is not very good in icy, snowy type conditions. Even a LSD or locked rear diff with no front drive engaged is a white knuckle drive in the snow or ice.
Think of an open diff like having one foot on the ice and one on the sidewalk, where as LSD having both feet on the ice. The tire that is not spinning in the snow or ice keeps you more stable and pointed "more or less" in the right direction.

 

This is true, but i plan on getting a car as a dd by the winter