Blender 2.7x has a Skeleton Sketching feature which I suspect is not used much.
//(mainly because we've had bugs in this area that weren't reported for years ... or at all, I found errors just looking over the code. eg: rB28f31bdfd807e35d7016623cc9af8467165a1052 rBa8487fc7fed94f1d658f8b6ccbe37473e6340a98 rB86a2e9d0e42ba1dbb31bf1e8cda94ea7db38544d)//.
My impression is that riggers normally want to control where their bones are placed with greater accuracy then you'd get from a sketch.
I'd be interested in feedback: are riggers using this and finding it saves them time?
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Note that I'm not against the ability to sketch armatures at all, it just seems the current code to do this, while quite advanced - is not being used much and could probably be implemented in a simpler and more accessible way.
Current skeleton //mode// with it's own drawing, operators, key shortcuts... etc. doesn't integrate into existing workflow well and from what I can tell.