For off-trail hikes, scrambling with a heavy load, glacier crossings, and cross-country marches, you need the support, weatherproofing, and durability of a burly boot.
Some clever scientist once determined that every pound on your feet takes the same energy to move as 5 pounds on your back. So it stands to reason that lightweight footwear will take you farther faster. But there are times when the light just is not right-when you’re lugging a big pack across steep sidehills, for instance, or descending loose scree and ankle-turning tussocks. Or perhaps you like climbing and snowshoeing, so you need better insulation and waterproofing, plus stiff soles for kicking steps, edging on nubbins, or attaching crampons. Or maybe your weak ankles and falling arches need extra-firm support. In all these cases, the ultralight mantra can be a false economy.