I think it is just as important, as a uniform, a car-topper, or signage. Your name on the box is an extension of your company. When the customer receives it, he generally rips of the box-topper, and saves it, and the box goes in the trash, or on the ground, or any number of places before it hits the recycling center or landfill. During its lifecyle the box will rack up a number of impressions, those impressions could turn into additional purchases.
In most cases, I have found that the cost of the boxes go down when I sign a contract with a manufacturer for the first 50 cases. The reduction in cost offset any production cost, and in some cases I have found the box companies will wave the setup charges, and plate fees if you place a large enough order, or long enough contract.
I think I was recently quoted $22.00 for a 50 pak of 16" boxes (Plain), and $19.69 (Printed), that a $.0442 savings per box, or a 3/10th of 1% savings on a $16.00 pizza. Small savings, but it all adds up.