Project Settings: Meanings?

I asked before but had little luck.

What do the project properties actually do? I have tried settings all over the place and they seem to make little if any difference to the rendered result. The only time I have seen a difference was when I set the AR of the project to a silly figure and got a strange AR rendered. Frame size otherwise seems not to affect the rendered output. Even the Best rendering quality setting is apparently over-ridden by renderers' settings.

I _think_ I did see a difference once when I was playing with interlaced stuff, where I git a better result by using Interpolate fields and not None or Blend. But as for the rest I cannot see how they interact with the render. Yet I am always being exhorted to get the Properties right, usually to match the source. But what if I am working from several sources with different characteristics? etc.

Any help appreciated.

Nick