I'm not Margo, but...I don't think shims effect the brake efficiency- they just mean it won't take as big a lever movement for the brakes to engage the rims. Your brakes won't be 'weaker'. I think by 'throw' she meant 'play'.
I have the shims on my Ultegra 9speed short reach brifters, and I just lOVE them. I feel so much safer now that my fingers can actually get a good grip around the levers.