"I want to rap/sing over your beat for my album and I want to be the LAST to buy it"
Exclusive Rights grant an artist sole ownership of the instrumental with unlimited sales. Exclusive rights guarantees that the artist will be the last individual able to purchase and sell the beat. Every exclusive purchase is bounded by a contract. Exclusives are generally more expensive but are a MUST have for independent and major label artists expecting to sell a lot of units.
"I want to rap/sing over your beat for my mix tape and I don't care if other rappers rap on it"
When an artist "leases" a beat they are granted access and limited rights to a producer's instrumental for a lower rate, for a limited time period (usually a year), and or a limited amount of sales. An artist can extend the life of their lease as well as upgrade to more premium licensing options until the beat is old exclusively. Multiple artists are also allowed to also lease and sell the same instrumental for a given time period and or until that instrumental is sold exclusively. Leases are generally for artists looking for high quality production to add to their mixtapes, EPs, freestyles, and other promotional content. Exclusives are generally suggested for artists working on albums.