When there are two Cost Items, one with Release to Warehousing applied and the other with Release to Warehousing not applied, upon approval of the Sales Order, the Cost Item that is released to Warehousing will go straight to Staged status, pending Shipment confirmation, while the Cost Item that is not released to Warehousing will be up for Sales Deliveries.
Apart from this main difference in functionality between having and not having this option to release to Warehousing checked, there are other impacts to consider...