Ha, fun discussion. Not surprised by the controversy. Some responses on the use here (I’ll come back to the substance later on):
I didn't invent this by any stretch (used a friends rack and liked the benefits). Here's someone else who does this: http://stephdavis.co/blog/racking-tips-for-crack-climbing/ Not that I’ll ever have close to her level of performance, of course.
One can suppose Steph has a few racks at her disposal and she's specifically talking desert crack climbing in that set of tips and half those cams are desert Fat Cams, so yeah, for desert cracks that setup probably works fine. But as a general practice at most crags, not a good idea. With rubber keepers? Not a good idea - Steph is using quite a few raps of tape in the pic.
Not really a matter of obsession, just a matter of what the pitch dictates. If you undersling the odds are good your cams are going to move in some manner. Like I said, I like mine to stay where and how I placed them. You may or may not care so whatever works for you.
I think you didn't realize what I was getting at. I agree with you that the rock/rope run dictates how/when to extend and I don't clip the rope directly to racking biner very often. My point above was that I see many (typically newer) climbers extend EVERY SINGLE 60cm they use.
If it's a straight crack in a corner with no change in pitch why are you extending it from doubled up? It serves no purpose, you doubled up draw is going to do an excellent job of keeping that placement from walking and not extending saves your second time. Now say there is a brief slab section, or you're pulling into a roof, THEN extend the sling. It makes sense to keep the rope run straight.
Nick, I entirely agree with you - sling to the pitch - that means don't unnecessarily under- or over-sling. Just because a sling can be extended doesn't mean it should be (though I haven't noticed folks always extending here, but rather usually no sling or not extending when it would be advisable). But overslinging will also bite you in the ass sooner or later. That's why a third of my draws are typically quickdraws - I still intend to sling, but I know I'm not going to need to extend them.