The limit of how far one can stretch out the foot of a shelf foot is governed by the foot boltrope AND the 'insert panels' of the shelf foot; there's only a finite amount strain you can put into a shalf foot before you start 'popping' the stitching, etc. Obviously you can more easily adjust the foot tension on a loose foot.

No argument from me as to which to choose as every Mainsail Ive lofted for myself in the past 25 years has been a loose foot (with apron).
I think also too that the non-stretch high tech laminates have dictated and driven the widespread trend to loose foot, as essentially with a laminate the shape that you build is the shape you get and no matter how much you 'strain the edges', ... other than the outhaul.