There are, however, significant downsides to those kinds of techniques. Most basically, you might wind up with deep stacks of hard to understand control layer gizmos. For instance, when you have gray masks on adjustment layers, the actual effect of of the control is somewhat obscure...it is less effective overall than with a white mask. With several of those things in effect at the same time it starts to become difficult to understand what control is actually controlling what effect. Adjusting one single partially masked control can require making compensations on several others.
I use the shadow masking trick a lot, but usually starting from a luminosity mask. The catch there is that you may find it necessary to create reverse masks to control otherwise easily managed stuff like highlights. And that inevitably leads to situations where in order to do just one more thing, you may need to regenerate several masked layers that weren't exactly right to start with.
There are other issues with hard edged shadow masks that may create artifacts in print sharpening.
But for relatively simple images as shown, those are good techniques. But there is still no truly free lunch.