Hi Mario,

> so what is the main difference between two identical spheres
>
> 1) created from the solids menue
> 2) created as sweep to identical dimensions

You won't really be able to do a sweep to the exact same shape as a pole, but you can make a sort of dome shape with the sweep.

The easiest way to see the difference is to turn on surface control points with Edit > Show pts.

For a sphere surface you can see that the surface control point grid has "poles" in it and how the control points compress together as they near that pole, like this:



On the other hand, if you create 2 crossing curves like so:



And then use sweep with one of them as the profile and the other as the rail to follow, it will build a type of dome surface like this:



And then if you select this surface and turn on its control points you can see that they are arranged in more of a regular grid pattern and the edges of the grid do not totally collapse down to a single point as a default sphere surface does:




If you want to avoid compression with Flow you'll need to use surfaces that are more like this in their structure - more evenly distributed and not having portions of the surface compress down to a point like a sphere does.

- Michael