There are more reasons than that. Millmax prevent your switches from resting directly against the pcb as they are meant to. Sound quality and rigidity are what you lose in that case. They also make your plate/pcb assembly less solid, which is obvious, but why does it matter? Your stabilizers are on the pcb, but the assembly is held up by the plate (top mount/ gasket mount), yes? So what is holding up the pcb? Friction. Each millmax socket holding on to each switch pin for dear life. If you press on a long stabilized key with fewer pins around it holding the pcb up (your spacebar), you can push the pcb down away from the assembly enough to contact the metal of your case and cause problems, or even separate the switches enough to stop them registering, though not many cases have that much free space. Millmax are best suited for keyboards that have a pcb supported from underneath, like a tray mount, or my tkc1800 which clamps the whlole assembly together from both sides. Now if you have a top-mount that you absolutely need to millmax, and you're not concerned with ruining your sound, or having a ramshackle barely held together keyboard, then you can place rubber bumpons or maybe some strips of foam under the pcb to prevent it from falling down.