Picking items from pallet racking takes time. Often a fork lift must be used to lift a pallet down before components can be picked. That means the picker standing idle while he waits for a fork lift driver.
Then the fork lift driver sitting idle while he waits for the picker. Not an efficient use of manpower!
Pull-out units at a sensible height mean that a single worker can get immediate access to the goods or components needed. There’s no waiting if the fork lift is unavailable, and no waste of staff time.