You may also have to pay for additional baggage charges if the combined weight or pieces of baggage exceeds your free allowance. (singaporeair.com)
With the airlines charging additional baggage fees, and overhead compartment space being insufficient to accommodate all the passengers, I'm guessing it's helped their credit card business. (creditcards.com)
View baggage allowances, purchase additional baggage, learn about dangerous goods or track lost baggage. (qantas.com)