smooth polygons essentially does what?

i thought it was for lower res characters to help hide the facets in the mesh.

i did turn off visible in ray tracing. i'll turn off smooth polygons too as suggested since the figure used is a higher res mesh.

should i leave remove back facing polygons on?

also i noticed that the first render i did was 3000 x 3000 but still soft as if blurry. what would have caused that?