First and foremost, if you are tied in with the rope, it is always preferable to belay from the rope loop.
However we dont always tie in (indoors, sports) and there are sometimes exceptions.
Let’s look more into this below, from the point of view of the belayer and the leader.
Indoor climbing/Single Pitch Sports climbing/Bottom Roping
There is no need for the belayer to tie in with the rope, so belaying directly from your harness loop is the obvious and safe thing to do.
Be sure to regularly check the stitching and quality of your harness loop for wear and tear and signs of degradation and retire harnesses when they become unsuitable for use.
You would expect the bolts/chains/anchors to be of solid quality in these instances and its of little relevance to factor in shock absorbancy on the system.
Just make sure to always tie a knot in the end of the rope or to a rope bag to prevent the rope from pulling through the belay device, there are numerous recorded instances of this occurring every year, causing serious accidents.
Single Pitch Trad Climbing
Belayer/second: Its a strong personal preference of mine that the belayer/second always ties in from the start and belays off their rope loop in this scenario. This is for two main reasons:
- Shock absorbancy: If the leader was to fall, belaying from the rope loop will give a little more shock absorbancy under loading. While you would expect the paid out rope to dissipate most of the forces created by the fall, in my opinion, on trad gear, every extra bit of shock absorbancy is wanted. Reducing forces on our leader placed trad gear is generally a good thing.
- Preventing incidents: On a few occasions I have seen the belayer not tie in, belay from the harness loop and the leader pull up all of the slack rope through the placed gear when safe. Perhaps unnoticed by the second as they put on their shoes. This isn’t a massive issue if the climb is straight up vertical, where the rope can be lowered back down to the belayer, but this can lead to placed gear being left behind. Mainly this becomes an issue when the route traverses or zig zags. Getting the rope back to the second and ensuring they are safe en route would be quite difficult and could lead to them taking a wild swing or even decking out.
Lead climber: Fundamentally, its safe for the leader to pick either option. Should a second fall the comfortable option is the most sought after and that is why we would belay off the rope loop.
The forces of a seconds fall on our body while belaying from the harness loop can be very unpleasant.
We dont really have to think in terms of shock absorbancy for the anchor system here, as in most scenarios the leader will have had time and space to make good anchor choices.
This might be different in Areas of poor rock quality. The last two times I belayed my second off my harness loop were at Murroughkilly and Oughtdarra. Both are areas where the rock is extremely friable and anchors are complex to build. In this instance I belayed off the harness loop as I want my body to be the first shock-absorber, then the rope system.
Mulitpitch Trad/Sport Climbing
Belayer/second: for the same reasons as above I would expect them to belay off the rope loop while on trad multipitch routes. Either option is safe for sports climbing multipitches, but the rope loop is again the preferable option. For incident prevention I would expect the belayer to be tied in from the very start.
Lead climber: While sports climbing its likely that there will be bolted anchors at stances and that you would belay directly off them, so this really isn’t an issue here unless you suspected your bolts to be compromised.
Trad climbing throws up a few choices though. If you have placed multiple bomber anchors and are swinging leads, I would preferably do as a single pitch leader would and belay off the rope loop.
If you weren’t swinging leads and the anchors were bomber, id either belay off the rope loop or more probably build a sling based system and belay directly from that.
But sometimes on a trad multipitch your anchor doesnt make you warm and fuzzy, so as a leader you would belay your second from the harness loop. It might be uncomfortable if your second falls, but it might just be the difference in your anchor holding or being compromised.
Every scenario is different and the above are general rules I try and follow as much as possible, but its also worth saying there are always times when breaking the rules is appropriate for the scenario, experience or further training will tell you when.
I hope the above info is useful. If you would like to discuss any aspect further, please get in touch and Id be happy to chat.