Aluminum is the most common material in mid-to-high-end alpine bindings, and for good reason. It offers an excellent strength-to-weight ratio, so you get reliable durability without unnecessary heft underfoot. It also dampens vibration well, which gives you a smoother, more predictable feel at speed and on firm snow.
The main downside is that aluminum can corrode over time, especially if you ski in salty coastal conditions or store wet gear. That said, most modern aluminum bindings are treated or coated to resist corrosion, so it's rarely a real-world problem for the average skier who takes basic care of their equipment.
For most resort and all-mountain skiers, aluminum construction is a solid, proven choice. It's not the lightest option for long touring days (composites win there) or the burliest for race-level punishment (steel takes that crown), but it hits a sweet spot that works great for the vast majority of skiers.