|Don's Home Recreation Hiking & Camping Equipment Snowshoes|
Snowshoes spread your weight over a larger area keeping you from sinking in soft snow.
They are also good for soft snow with a hard crust where postholing (breaking thru the crust) can make hiking miserable. You have to shorten your stride to pull your foot back up thru the hole and avoid bruised ankles where they hit the crust as you stride forward.
In powder snow deeper than your knees even 30" snowshoes will not keep you from sinking. It is best to use skis or let someone else break trail. (BackpackingLight.com Forums)
The amount that bindings pivot varies among models. Some bindings are attached with metal rods and pivot 90° or more. This causes the ends of the snowshoes, called tails, to fall away as you step, shedding snow and reducing leg fatigue.
Heel lifts: Also known as climbing bars or, on MSR models, Televators, these wire bails can be flipped up under your heels to relieve calf strain on steep uphill sections and save energy on long ascents. This feature gives the feeling of walking up steps and prevents exaggerated calf and Achilles strain.
Sometimes you only need a little larger footprint to keep from postholing.
Running snowshoes typically have lighter-weight construction and bindings than your average snowshoe. The bindings are designed with running shoes vs. boots in mind. There is typically an extra cleat under the toe for additional traction while running on packed trails.