In my opinion saving your LB is only worthwhile in certain situations where you want to get past a specific phase or avoid a specific mechanic. Other than that I don't see any reason not to use it right away, provided you have a good group who knows what they're doing and don't need the healer lb safety net. Really the only time I've seen that safety net work anyways was when dps dying was the problem, if your tanks and healers are dying then you might as well restart in most cases.