I like it when the status effects can be used on bosses in unconventional ways to give an advantage but not trivialize the fight. For example, if a boss does not cast any magic other than a massive cure spell, Silence would make the fight easier but not trivial. Or perhaps it keeps respawning minions which may be better to put to sleep instead of constantly killing. Or maybe Blind works for a few seconds and you can use it to avoid it's most dangerous physical attack with proper timing. I always felt the status effects in FFXI were pretty useful on certain bosses in this way.