If you ever snowshoe, backpack in the snow, or climb to mountain peaks that are covered in snow, you’ll want to treat the leather on your mountaineering boots to make sure that your feet stay nice and dry.
All good mountaineering boots will have a Gore-Tex or other waterproof lining that will keep your feet dry, however, that doesn’t prevent the leather on your boots from getting saturated and weighing you down.
I highly recommend using a waterproofing product like Tectron Sno-Seal on the outside of your boots, before you head to the snow. It may darken the leather a bit, but snow and water will bead up on the outside of the boot and keep it away from the Gore-Tex liner. I put on Sno-Seal on my La Sportiva Glacier Evo mountaineering boots a day or two in advance of every snowshoe trip and winter hiking expedition. Water just beads up on the outside of my boots!