I believe they mean that when you install a sink (for example) with new countertops, you have to cut the sink out (obviously), leaving a sink-shaped "blank" leftover that the contractor doesn't need. Instead of tossing it out, the countertop installer might be able to shape it to the size of your table and use it that way, saving waste on his part and costs on yours.
It could happen. If not, getting a piece of the correct size custom cut and beveled will still not be a bank breaker, plus it will increase the value of your table. Without the top, your table is worth about 10-20% of what it should be.