The one tactic that is botched 95% of the time….

….the grubber kick. Potentially a devastating response to the rush defence, the grubber is routinely kicked too far and so, easily dealt with by the back three. Most of the time the grubber should go no more than 10 metres, to allow your backline a 70/30 shot of regathering as their opponents turn  and thus breaking the line. 
My guess is it’s a field position thing. But 25 metre grubbers are a dead loss unless the defence is totally out of position. And usually results in a field position loss without producing any threat. 
Done right it’s a great surprise  tool in these mammoth phase play segments. But the kicker has to move into the gap so he and the ball have a path through, and it needs to go a short distance.
Make a point of checking the grubbers and see how many go too far for the kicking team to ever regather.

It’s a difficult kick to weight perfectly as often the kicker is moving while having to execute - plus given the nature of a rugby ball one can never be certain of its end result It does seem to be used more often these days - Fassi’s grubber through for Mapimpi’s try this past weekend was a perfect example of its effectiveness

Indeed, rather too short than too long. At least if it’s short, the opposition backs are collecting the ball with their back to you. A big hit, while they are moving backwards, followed by a quick ruck to draw the penalty or regain possession. Momentum.