That 1200 A frame means it handles the full feeder current for a large motor control center or a main distribution panel — the kind of breaker you spec once and don't think about again, as long as the coordination study holds.
The E.DIP LS/I trip unit gives you long-time and short-time pickup and delay adjustments plus instantaneous pickup — selectivity tuning for downstream breakers without swapping trip units. On a 1200 A frame that's the difference between a nuisance trip on a motor start and a coordinated ride-through.