As with most items, a minimum of 0.125" or 1/8" margin should be allowed from all cut edges. With Brochures, all important content should also be a minimum of 0.125" or 1/8" from all folds. This is for aesthetic reasons as well as practical ones. Suppose there is a nice even margin around the content. In that case, it will be pleasingly centred on each panel and it will look more professional. It also helps delineate the content on each panel. It makes sure that nothing will fall into any of the folds or run over onto another panel. This can be especially problematic if the panel in question is on the outside, and the content runs onto one of the inside panels so that it is only fully visible when the brochure is unfolded.