Three-buckle boots are a great choice if you're primarily ski touring or heading into the backcountry. By dropping one buckle, you save noticeable weight on the uphill and enjoy faster, easier entry and exit during transitions—something you'll really appreciate after a long skin. The closure power is still plenty for most skiers on the descent.
That said, if you spend all your time at the resort, you'll likely prefer a traditional 4-buckle boot. The extra buckle gives you more precise adjustment across your foot and lower leg, which translates to better power transfer and control when you're laying down carves or charging through chop. For pure inbounds skiing, the small weight savings of a 3-buckle boot isn't worth the trade-off in performance.