It provides the quilter with a larger level surface to arrange squares on, whilst sewing.
Thrown together in a morning, it uses 10mm thick acrylic for the top surface, into which I cut the outside profile of her favourite sewing machine.
Step 1: First measure your machine.
You need to measure, reasonably accurately the profile of your machine at the level of the platen. I'd make a template to check the design fits !
My table size was limited by what I could fit into my laser cutter, but you don't have to use a laser, and you don't have to use acrylic, but it does look pretty.....
I also added a series of parallel engraved lines to the platen, 0n 12.7mm, 1/2" centres, as a sewing guide - so the long lines you see DON'T go through !
Step 2: Cutting.
If you use acrylic "by hand", you can scratch the guide lines in with a piece of hacksaw blade, sharpened into a very thin chisel.