While I agree that there are bosses that you should hold the Limit for... in some dungeons there's absolutely no reason. I've been in dungeon runs where I politely held off on using the limit cause the other DD was a melee... and they never used it against the first two bosses. So I'm of mind that, if we fill the bar well before a boss gets to 20% and it's left to sit till that 20%... I'm using it. It's rare that those first two bosses have some manner of sneaky mechanic that can't be thwarted by anything less than a Limit.