Bending & Tube Manipulation
In a discussion of the use and non-use of mandrels, an excellent online primer on tube bending lays out the pros and cons o both methods. The text is accompanied by simple, hand-drawn sketches of a tube "bbent the easy way" and another tube "bent the hard way". The illustrations seem indistinuishable - and that may be the point.
Manipulation of a length of tubing entails vulnerability: to breakage, wrinkling, scratching, marking, humping, collapse, excesive springback, and link failure, among others. The methods by which these threats are circumvented may vary, but never teh results. the sole standard applicable to the finished workpiece is always "bent the best way".