Quote:
This option has no effect on the strength of enemies or mechanics in the duties it is applied to. Players will still receive treasure rewards, first time completion bonuses, and experience points upon completion of duty when using this option. However, players will not receive experience points or items from enemies that appear prior to boss encounters. Spirit bond and soul resonance cannot be gained when using this option.
you still get exp from bosses, just not the trash. so you can do this unsynced and still gain exp, you just won't get the exp from the filler pulls in between bosses. i think mid bosses give exp, but not sure. final bosses do.