Hey Doug,
the advantage of the QCW frame is that it includes the Any Surface Leveling Feet which allows to adjust coplanarity of the machine. If you bolt it down to a tabletop, you cannot use this feature anymore.
Setting Rectangularity and Coplanarity of a gantry-type CNC machine is important, otherwise all your workpieces may result in having no right angles (being a parallelogram instead of being a rectangle) and not being flat (but twisted).
Before such a machine is ready to use, it is therefore necessary to make sure it is 1. rectangular (“squared”) (bar gauge) and 2. coplanar (“not twisted”) (fishing line method).
Surfacing the wasteboard does help nothing if the machine is not accurately rectangular (“squared”) and coplanar (not twisted). All your workpieces including the wasteboard will remain a parallelogram and have a twisted surface if you didn’t ensure that steps 1 and 2 are done accurately.
Furthermore, if rectangularity and coplanarity are not perfect, the Y movement can block or have “hiccups”.
You may however use other methods to ensure coplanarity, e.g. height-adjustable casters on your table’s feet.
The QCW Frame has some disadvantages though. It is rather expensive and reduces the X/Y workarea because there is an area at the front where there are not wasteboard slats. At home position (X=0, Y=0) there is no wasteboard under the milling bit.