A backpack vac has some distinct advantages in a large commercial setting; movie theatres, banquet halls and churches come to mind.  In a home setting I can see where a professional cleaning service might employ them, but the typical models designed for home use have a couple drawbacks in my opinion.  The bags are small and tend to plug up with dust quickly.  The opportunities for "bumping tragedies" abound.   I much prefer a cannister which follows obediently when tugged but the weight rests on the floor, not me; with a reasonably long hose permitting standing on a stepstool to reach high shelves or cleaning a staircase without needing to lift the machine. 

Case in point:  My mother has an Oreck "team."  The upright works well for traffic paths, but the portable cleaner with its short hose was a consumate nuisance.   I retrofitted a long hose on it for her so the machine can rest on the floor and now she can go about her tidying-up without bonking into things or struggling with that stretchy hose which would keep yanking the machine off her shoulder.

Whether it's an all-in-one machine, a "quickdraw" upright, a Dialamatic/Pannasonic/Riccar style upright with detachable hose, a cannister, or a "team" of machines,  no single arrangement is going to satisfy everyone.   Personal cleaning habits/routines will determine which arrangement suits that individual.   Viva la difference!