Yes, it is necessary, especially with a roller. There are two factors in this requirement: the first is that if you use the sail well rolled up you put the whole load from the sail near the middle of the stay, and this results in greater angular deflection than is experienced with the distributed load from hank on sails
. The second is that the considerable mass of the rolled-up sail puts a lot of stress on the stay simply from rolling and pitching of the boat. The toggle is quite a bit more flexible than the stem ball, and there will be less wire fatigue accumulated due to that flexibility.
I believe that any rigger will agree with the requirement!