The bad part is you are forced to play always the same job. For Novus you could do the expert roulette with different jobs for a change and dig the mysterious map with other, then use the alexandrite for your main's weapon. Also for example in ST you have to go with a job that probably doesn't need the loot, instead of upgrading the alt classes mainly in ST and the main class with soldiery.

I used to enjoy doing content with different jobs, now I feel I'm wasting time if I don't use the main one in most content.

Good part: you find best geared and experienced players all around. ST runs are much better now as they used to be, everybody that needs the Nexus is playing their main job. Same in Expert Roulette.