To include white space is a decision that the art director should make. It will be based on an anticipated sense of how all of the ingredients, especially volume of copy, will work. Those who expect a poor reaction because the proposed size is so small that it will look choked and be hard to absorb will need to consider adding air.
Naturally, if you have put the brochure in the hands of your target audience, they are already predisposed to learn more. So maybe the extra cost for white space seems excessive. However, giving a competitor the chance to be remembered fondly, instead of you, for the sake of a small savings is a mistake. Because, putting a communication in the right hands does not guarantee results. The quality of the piece and the feeling it evokes are part and parcel of its chance to succeed under any circumstances.
Art direction, creative direction and design*