I can't imagine it being a true "need" as opposed to a somewhat extravegant convenience but maybe it is for LA quilters who buy batting on the roll. They could measure out the amount they need and rather than cutting with scissors (which is what I do) they can lay it out on the table behind the machine and cut with a ruler and rotary cutter. They may also do that with wide backing to ensure a nice straight cut.
Can also be used for squaring up quilts.
All these things can be done with conventional tools. This product just may make it more convenient. I for one would rather spend the $150+ on fabric, thread or batting.