What are the key benefits of the non-refundable deposit fares?

The key benefit when booking non-refundable fares is lower pricing. 

Guests who take advantage of non-refundable deposit fares prior to 1 November 2018 will automatically earn an onboard credit of up to US $100 per stateroom. Those who book non-refundable deposit fares on or after 1 November 2018, will no longer qualify to earn an onboard credit.