How do I know a fabric marker will come out?

Test on a scrap of the same fabric before you mark the quilt top, every time. Removal depends on the fiber and the finish rather than on the pen. A marker that vanishes from quilting cotton can set permanently on a coated or heavily blended fabric.

Why press on wool rather than an ironing board?

Wool holds heat, so the mat presses the seam from underneath while the iron presses from above. Seams go flat in one pass and blocks finish squarer. It also protects the table underneath, which is why quilters end up pressing beside the machine.