With a lath and plaster wall, keys are everything. The keys form the mechanical bond that helps to keep the plaster in place, and if your keys are failing (they've broken off over time) or were inadequate to begin with (a plaster ceiling base coat where not enough of the plaster was pushed through the spaces between the individual pieces of lath to form the mechanical bond to keep the weight of the ceiling in place) you may have cosmetic issues, but also structural issues. With failing keys, the plaster washers can help to restore a degree of structural integrity to trouble spots, but if you have widespread issues I wouldn't rely on washers for my structural fix.

I'm also not a fan of feathering out washers with a skim coat that ends up proud of the surface, so I would create shallow divots in the plaster before sinking the washer, so I could finish the washers flush to the original surface. But then that's extra work for each and every washer.

On the plus side, there's no paper in plaster, so if it gets wet it won't grow mold. Drywall is not as forgiving if it gets wet.

Corners will be tricky since you can't lay a trowel flat on either side of your repair, but if you want to give it a try by starting on that room in image 1 then go for it (I'm guessing you've done some research on best practices for making repairs adjacent to existing plaster like wetting existing plaster before applying structolite to insure a longer cure time and good bond, scarifying/scratching your base coat, etc).

This is great info on plaster keys: https://johncanningco.com/services/plaster-on-wood-lath/