Walk mode is a mechanism that unlocks the boot's upper cuff from the lower shell, letting your ankle flex forward more naturally for hiking, skinning, or just walking around. It's absolutely essential if you're doing any backcountry or sidecountry skiing where you'll be hiking to earn your turns.
That said, walk mode isn't just for touring skiers anymore. It's increasingly common on all-mountain and freeride boots, and many resort skiers appreciate the convenience when walking through parking lots, navigating lodge stairs, or hiking to a lift. It makes those awkward boot walks significantly more comfortable.
If you strictly ski inbounds and don't mind the stiff, clunky walk of a traditional alpine boot, walk mode isn't a must-have. Just know that once you've experienced the freedom of a hike mechanism, it's hard to go back. One important habit: always double-check that you've switched back to ski mode before dropping in—forgetting this is a common and potentially dangerous mistake.