A 2-0 lead is not enough to start sitting back, especially when that lead is achieved very early. It merely encourages the opposition to believe they can still get something from the game. Complacency is provocative. And, as Jazz says, once you lose the initiative, it is near impossible to regain it.
Also, far from conserving energy, it actually increases the risk of injuries being sustained. Injuries most often occur when players are operating below their full capacity. They go into tackles with their muscles relaxed, which is apparently the easiest way of getting yourself injured.
I don't think there's any excuse for slacking until at least a 3-0 lead has been established, and even then it shouldn't be done unless there is less than 30 mins left.
Also, far from conserving energy, it actually increases the risk of injuries being sustained. Injuries most often occur when players are operating below their full capacity. They go into tackles with their muscles relaxed, which is apparently the easiest way of getting yourself injured.
I don't think there's any excuse for slacking until at least a 3-0 lead has been established, and even then it shouldn't be done unless there is less than 30 mins left.