In reply to Oceanic: I use the cordaleette method for making anchors. Quite often when I set up an anchor and start belaying I then notice that the ropes pull the anchor in a slightly different direction than anticipated and 1 or more legs are not as loaded as the other(s). A piece of gear that is 180 degrees to the direction of load will be loaded far more than a piece that is say 120 degrees to the load direction, even if equalisation is perfect. If you put a cam in your belay and the system is moving a bit as you belay, it will often move a bit in the crack. There are, in short, loads of different ways that the legs will be unequally weighted and frankly I don't think anyone short of a rope access tech using bolts builds an anchor that distributes precisely equal loads to every point (I guess you can get closer with the sliding X but I don't like it for at least 2 reasons*). None of this matters though because you should build every anchor so at least 2 pieces are absolutely bomber and even if one was to fail, the remains of the anchor could still take more load that you could ever put on it with a second falling off or the belayer dicking about. It is best if the belayer attaches to the cordelite with a short section of rope so any load they put on the anchor is damped by a bit of dynamic action from the rope, this will ensure any loading of the anchor by belayer or second has rope in the system to absorb shock.
If you are building a very marginal belay then the exact way you do it, with rope or cordelite, will depend very much on the placements you have at the time and possibly how well you think your bum is adhering to the rock you are sitting on!
* 1) If any piece fails, at least one other piece is shock loaded.
2) In my head, at the time of placement failure, the 'X' where the sling crosses itself moves very quickly while under considerable load. My knee jerk reaction is to not like nylon rubbing against other nylon under load and at speed. It's a gut feeling and I'm perfectly prepared for people to call me out on it.