Exclusive licenses make the purchased track a "work for hire". In a work for hire agreement, the seller (producer) loses all rights to their beat, including the copyright and the right to use the beat again for any purpose.
If, on the other hand, the grant of rights is a non-exclusive license, the producer keeps the copyright, and retains the right to use it or make other deals.
Even in the case of an exclusive license deal, all other previously granted licenses remain valid until they expire.