I can definitely see the merit to this early on. Where simple monsters give you 200-300 exp per kill, and where a FATE gives you perhaps 4k exp at most.
I'm pretty sure once you reach coerthas and get 10k to 40k from some of the 1-2 minute lasting FATEs, there's really no point to this anymore.
Still, this whole exp mentality has been happening ever since XI. People absolutely refused to kill anything but the Incredibly Tough monsters, which netted the party 600 exp in a chain. While they could have simply been mass-killing lower level monsters for 200 exp per kill, just 10 times as fast. It wasnt till the later years that they finally realized that "Oh, we make more exp just killing trash".
____________________________
[XI] Surivere of Valefor
[XIV] Sir Surian Bedivere of Behemoth
http://na.finalfantasyxiv.com/lodestone/character/2401553/