What UVs would you use for full-screen effects? Typically you are only interested on the screen position to sample relevant buffers, i.e. gl_FragCoord or interpolated vertex positions depending on what scale you want.
That’s true - not so much UVs, but texture coords I find are useful for quickly flipping the screen horizontally or vertically - so storing both a vertex position and a x,y value 0-1 for sampling a texture. I guess could just interpolate the vertex positions directly, just it’s less intuitive with a large triangle.