Hi @arcangel_zero7 ,
In regards to Q1, What you would look for when deciding when to use this normals fix, is the weird shading like in the lesson. Knowing when to use it comes from experience, and would depend on the use.
If you want to see a different use for this normal trick, see collab2021-week-3-casual-live-stream, from about 52 minutes Kent creates a bush, and uses this to change the shading on the bush.
And again for clouds in collab2021-week-4-finalization-live-stream from around 35 minutes.
And Q2, You are right, for efficiency in a game you would bake your normals onto a normal map.
If you want to know more about normal maps for games then take a look @jlampel ‘s Normal Map Modeling for Games and also Creating Animated Sci-fi Game Assets.
Happy Blending.
