Also once you have a good idea of what works well for smooth polygons for a given shape, it can be helpful to use the vertices>weld>target. Thsi way you can weld specific vertices to others to reduce poly counts. You remove 2 polys every time you weld 2 vertices together.
I don't use the poly reducer tools much since I usually have specific ideas on how I want the shape to go. This can oly be done manually if you want real control.
Another thing is if you want smooth curves. An edge that is like the edge around the saucer on the Enterprise, requires a lot of polys to smooth out the edge, But, the next row in can be i/3 or 1/4 of the number of polys and still give the smooth slightly curved surface without bumps, or apparent straight lines.