I have used this technique on occasion for pieces on lead. Â Basically, it is an act of desperation, and even as I set this sort of thing up I know in the back of my mind my time is better spent climbing and I am just being a weeny. Â Usually, there are ice screws involved and some running water. Â Nevertheless we all have our stupid little ways to procrastinate while doing a lead and this is a beaut. Â You can put off climbing for at least 10 minutes on ice - and if rock is your medium, then you're in heaven. Â A determined procrastinator on rock could easily eat up 20 minutes once the brass nuts and other fussy pieces make an appearance.
As an anchor, I think it is a total waste of time. Â Presumably, you would only need to do this on 2 sketchy pieces. Â Whatever you gain by loading each piece perfectly, you lose that much more by shock loading the remaining piece. Â The ironic thing is that even if the forces are minor in regard to the extension, if your gear is so sketchy as you have to actually go through the machinations of having to equalize 2 pieces to get them to hold, that means the shock loading of the 2nd piece would probably cause it to fail. Â For this, you give up redundancy. Â I am a huge fan of redundancy. Â I am a huge fan of redundancy. Â (sorry I couldn't resist). Â Lastly, you can get pretty good pseudo equalization if you stick a knot in the system. Â The good thing about an anchor is you have a pretty good idea where the direction of fall and forces will come from and anticipate accordingly. Â A well placed knot will get you 95% of what perfect equalization will, without the drawbacks.
If both pieces are bomber then it is a total, total a waste of time. Â By doing this you are now making the sling a single point of failure (although I will admit that this is *extremely* unlikely) but why bother?
Lastly, if you mess up when you put the half-twist in the sling, you're not actually inside the sling. Â This means if one piece fails, your actually not in the loop and you die. Â It is hard to determine whether you are in or out of the sling by visual inspection. Â Yes, this should never happen to a competent climber, but sometimes it does. Â So again, why bother?