The benefits of salting before a snow storm are a few, being the most important not to allow the snow to stick to the driveway or parking lot material.
in small storms the salt will melt the snow as it falls or at least reduce the snow accumulation, the grains of salt will also serve for traction until they are dissolved by the moisture in the snow.
The big benefit comes after plowing the snow because there will not be thick layers of compacted snow or ice to be removed.
the reason you may have noticed some lines on the highways or local roads before any predicted storms is because liquid salt has been applied to them to prevent the snow from adhering to the road surface.