The old EXP/Merit systems allowed players to level up and max out a Job without ever having to play it. Overnight, a player could go from BRD30 to BRD99 with max merits and be nearly indistinguishable from someone that's been BRD99 for the last year. The Job Point system rewards people for playing different jobs by allowing them to get better at the Job (statistically) as they continue to play it. Likely as a result of the Job Point system, I've seen a few people are pretty regularly do Delve1 as jobs like BLU and RUN.