What does the Masks in Layer Control do?

Some Effects reference other layers to create their magic. Most, but not all, have a pulldown that allows you to work around the top-down rendering order that After Effects uses to calculate pixel data. If the reference layer has masks, they are ignored by the effect unless you Select the Masks or Mask and Effects options. This allows you to have more control over the effects.  Layer Control is an Expression controller that links the values in one layer to the values in another for the same properties. Here's a tutorial that explains how to use that controller: https://lesterbanks.com/2015/06/layer-control-after-effects/