Steel bindings are built for maximum durability and strength, making them a great choice if you're pushing your gear hard. You'll see steel most often in race bindings and heavy-duty freeride setups where forces are intense and reliability is non-negotiable. If you're charging big mountain lines or racing gates, that extra weight is a worthwhile trade-off for confidence that your bindings can handle serious abuse season after season.
For most resort skiers, though, steel is overkill. Aluminum and mixed-construction bindings offer plenty of strength at a lighter weight, which translates to less fatigue and easier turn initiation. The weight difference becomes especially noticeable on long days or if you're doing any touring.
Bottom line: Go steel if you're a competitive racer or aggressive freerider who prioritizes durability above all else. Otherwise, a well-engineered aluminum or hybrid binding will serve you just fine without weighing you down.