Pallet shuttles enable much denser storage than conventional racking because there's no need for a forklift aisle beside every lane — the shuttle does the work inside the lane itself, on a rail or channel built into the racking.
The failure consequence differs sharply by architecture. A deep-lane, LIFO-style layout with a single shuttle per lane strands every pallet behind a stalled unit until it's physically recovered. A fleet-based pool sharing a grid routes around a failed unit instead, typically losing single-digit-percent throughput rather than stopping the lane outright.