The B/L does three jobs: it acknowledges that the shipping line received the goods, it evidences the terms of the contract of carriage, and it represents the goods. Whoever holds the original can claim them at the port of discharge, which is why it secures documentary credits.
It can be straight (named consignee) or 'to order' (endorsable). When the title function is not needed, many lines issue a sea waybill or a telex release, avoiding paper originals. A forwarder usually issues a house B/L under the line's master B/L.