It's also a performance hog, rendering-wise, regardless of normal maps. Long thin triangles are harder to rasterize (turn into pixels). Some good reading over here: FAQ: Game art optimisation (do polygon counts really matter?)
What is pixel shader overdraw? Are you implying that that are no problems with shading issues on low-poly models what-so-ever if triangles lie on the same plane? Just want to cross that off my list of things to worry about if i can.
In the context of long thin triangles, it refers to the waste of shading processing when you have a surface that's not triangulated with care. As a necessary step, a GPU will process triangles in a way that is efficient when rendering the interior of triangles, but not so efficient when rendering the edges of triangles.…