Hi Lordfox, if you still need more information can you please post the 3DM model file where you didn't get good results so I can look at what you're trying to do there?

The "planar sections" option does not mean to use it between planar sections as the input edges, it means to make the blend create all planar curves for the cross sections that are used to calculate the Blend. Blend constructs a surface basically by lofting through a whole bunch of automatically constructed profile curves that attach between the 2 surfaces. When these profile curves wiggle around it can tend to make lumpy results in the blend. The "Planar sections" option tries to instead make each profile curve go on a single plane and that tends to make them wiggle less and can help avoid them from pushing through each other.

Usually it's used when connecting a closed tubular type surface like a wing shape onto a main body as shown in that previous example:
http://moi3d.com/forum/index.php?webtag=MOI&msg=6790.35

re:
> and I didn't see sections

That's normal that you won't see separate sections displayed - you will only see the Blend surface displayed. The planar sections option just modifies how the blend surface is constructed.

- Michael