however I think Will missed one important point about why many of us clip the anchor before leaving, and that is direction of the following pitch.
As much I agree with Dman that reading anam is important for safety, as much I think that confrontation to improve our knowledge. Some one can think that it is a fight, but I think that it is more a friendly discussion to be better climber. if you remember the theory behind the discussion, if we agree each other on some point honestly, what will stay is some think that can save your life.
Should I disagree with Dman on the direction of the following pitch...
If my leader fall on the right, I will hang on my left foot and turn to the right so, my device will be in the good direction. If he fall on the left, I will hang on my right foot and turn to the left. I will always have the same breaking hand, my right, which is stronger. If the slope is close to 90 degree, I will let some rope to go true the device to have a soft belay (see the term) if the slope is 70 degree, I will try to avoid any slippage of the rope to the belay.
the reason of that is not as a belayer, but as a leader. When you lead, you arrive at the top of the pitch and you will built your anchor. Did you clip just one bolt? No, at least two... and often more. You are not going to place just two pro, but also a back up to prevent the belayer to pop out the anchor in the case of a leader fall with one pro. When you have two bolt, you equalize them with a sling. You like that two bolt hold your weight and a fall when your partner lead the next pitch. As your second climb, the forces on the belay in a fall is very close to his body weight (one or two kilo newton). You want a strong belay only when you lead... that is the important point.
As a climber, what do you want? You want that an anchor will hold the most important fall in any situation. Imagine hanging at the end of the rope with no anchor, even in a "standard" slab, and you know: it will hurt when you will touch the ground. The anchor is the most important think in your life when you climb (exception of running belay, why not running anchor? there is a reason).
Let put that in number. Fall factor two generate a maximal force of 12 Kn (I don't remember: uiaa standard or some think). if you fall on one bolt who hold 24 Kn there is no danger. If the bolt is weaker and hold 10 Kn the bolt will pup out and the second one, place in the same rock, will do the same, your death. If you have two bolt, equalize with a sling of 16 Kn, less the weakness of the knot, you can hold a fall factor 2 (12 Kn) with two stopper of 6 Kn each. that means two stopper number five.
Dman, I will be honest. I didn't understand any thing of your explication. Could you say the same for mine?