I want multiproduct discount

Why and when should I check this option?

You should check this option if your machines do not have an internal floppy disk drive and you would like VNI send one external floppy disk drive with your software.
Instead of sending multiple external floppy drive, you can use this option so VNI will not send you more than one floppy disk drive, therefore saving you extra external floppy disk drive costs and shipping costs.