I presume that the main one is that less players are committed to the breakdown in attack and hence the attacking team has more players out wide to create overlaps and take advantage of space. There would also be less chance of getting turned over/pilfered if you successfully seal?? I am correct?

2. Reduces contest for ball.

3. Choice about when to release the ball from the ruck.

4. Less men committed (as for 2.).

5. Creates a ruck situation (I know this is not technically true) - meaning that the referee is more likely to penalise the opposition.

Collectively these adavantages favour a wide multi-phase game (Australian). I disagree with those people say that sealed ball is necessarily slower - it is on average, but not massively. A clean-out rucking style (no sealing) favours the pick and go style (from the base of the ruck), and can be good for providing some go forward, however it is very vulnerable to turnovers, and lacks width. If you practice 2 or 3 phase patterns you could use clean-out rucks on these, assuming that your players will be their first as there are no decisions to be taken.

Both styles can be negated by getting two defenders into the tackle, and slowing the ball down this way.

A way of adapting to the new rules is to use a hammer (i.e. supporting player binding on to ball carrier). He can then go to ground with the ball carrier, in a protective fashion, which at the least buys you some time.

What are the technical aspects of sealing? I would presume putting your arms and head on the far side of your player who is on the ground (whilst staying on your feet). This will prevent the opposition from getting to the ball.

Surely speed of the breakdown has more to do with ball placement and halfback availability than wether the clearout man cleans past the ball or stops at the ball to seal?

If they are going to seal a ruck, I don't want their head/neck in a bad position, I want their backs/shoulders slightly above hips - I just want them strong and safe.

I've found that most people who put themselves in the dangerous head down, butt up position don't really have the flexibility to get into a good position while being low enough to do the deed.  Hips, hamstrings, lower back - lots of stuff you can look up, and I've even started passing on yoga and pilates stretches (but not telling the lads that!) for them to do at home. 

In fact, it was my softening on the idea of doing such things that helped my own back issues - the downward facing dog being particularly useful.  (Reason #13 I no longer belong in the front row union - BUT, I've seen some GP teams do things in pre-game warm ups which are essentially yoga moves, so we all have to come around sometime.)

An old, particularly effective, way of sealing was to place the back of your head on the stomach of the tackled player and grip his shirt with your hands. With the new refereeing climate I doubt this is wise, but it points towards the key aspects of succesful sealing:

1. Your body is between the opposition and the ball.

2. Your body is in a stable position.

3. The ball is not past your hindmost foot.

My way of incorporating these three demands and the current interpretation of the laws is to have the sealing player bind on the player on the ground but still supporting their own weight. This is easy enough.The sealer has his feet significantly offset (one quite close to the body and one much further back) allowing the ball to placed away from the front of the ruck, and is so low that it is very difficult to get under him to push off the ball. If he is pulled forward then he is still in an effective position. However any technique which accounts for the key factors above should work.

I hope this is clear enough!

2. "Surely speed of the breakdown has more to do with ball placement and halfback availability than whether the clearout man cleans past the ball or stops at the ball to seal?"

Yes, these are key factors, but the pile up of bodies that can result from players sealing can also be significant at times.

Also you are in a weaker position as the player on the floor isn't stopping the defensive ruckers placing their feet close to yours.

The key at the breakdown must be keeping players on their feet.

Personally, I don't see how referees are going to stop it: too many players do it; and even those who do not have the intention on stopping over the ball end up doing precisely this. These players often end up in even worse positions (lying on the ball). This is beacuse the one consistent element in rucking styles is getting lower than your opponent. Munster (who must be one of the faves for the Heineken) nearly always end up creating static ruck situations with piles of bodies. Referees don't allow players to come over the top in situations like this, nor say that the ball is out, which I thinkk it technically must be (if all the players are off their feet). I am not saying this helps the game as a spectacle - I'm just trying to be pragmatic.

I attach a link to a video where Eddie Jones provides a commentary over footage from the recent Viadana game. As well as being an interesting watch, it also shows that Saracens' game is firmly based on a sealing approach. They also utilise the hammer to get a supporting sealing player first to the breakdown (e.g. 1.04, 2.07), which I talked about in an earlier post.

Hope this is of interest and doesn't appear like point-scoring, which it's not meant to be.