In reply to CCob:
What is the difference between belaying from the top off your harness and belaying off a fixed anchor point next to your anchor point? Nothing (except that it is easier to escape the system in the latter case, and the load will not go onto you).
The advantage of belaying off your harness is that you will always have the belay plate in a position where you can safely belay with it. This is not true for all anchor points, but that doesn't invalidate direct belaying off a suitable anchor point. Similar (but possibly less critical) concerns apply to the placement of a guide mode plate...
Guide mode is great for bringing climbers up, but it is NOT a great solution for lowering. If I found myself next to a suitable fixed anchor point and knew I was likely to have to lower but also wanted to be able to easily escape the system then belaying in non-guide mode directly from the anchor is probably the better solution. As already described, redirecting the brake rope through a krab on the anchor makes lowering easier.
This is _not_ a normal situation. Normally in trad a) you aren't expecting to lower, and guide mode is usually the better solution (or a standard belay off the harness for simplicity). This is IMO why you rarely see this. I do often belay direct off a quick belay when moving together but I just use an Italian hitch since I am not expecting the rope to be loaded.
To respond to something in the OP, it doesn't matter if you sit down/bend/stand up to belay if you are not part of the system (i.e. are belaying directly off an anchor) as long as you can safely operate the belay plate and you will not shock load the anchors if you slip - ideally with no slack in your cowstail and do not climb above the anchor. For anything other than a bottom belay, the correct choice of position (sitting, standing etc) depends on the position of the anchors and the expected load. Sitting down is common at the top of a route, standing on a stance with high gear.
Let the debate continue...
Post edited at 21:26