Explain this number please. I have 2 Clipping attachments. right one creates one polygon, left one I assumed will create 3 extra but it shows 6 total, where do other 2 come from?
Clipping polygons in Metric View
The number of clipping polygons shown in the Metrics view represents the total number of convex polygons created by your clipping attachments. When a clipping attachment has concave vertices, it is decomposed into multiple convex polygons.
In your case, you have two clipping attachments. The right one creates one convex polygon, while the left one, which you assumed would create three extra polygons, actually results in five convex polygons. This means that the left clipping attachment's vertices are decomposed into five convex polygons due to their concave nature.
For optimal performance, it is best to ensure that each clipping attachment is convex, resulting in fewer clipping polygons. You can find more information on clipping performance here.
First of all, WOW to Spinebot I am amazed how to the point your response was! Did you actually read the image or just assumed that from my text.. anyway I want to see how it cuts that simple polygon into five convex polygons. it does not add new vertices right?
Yeah sometimes Spinebot nails it! 
I highly doubt it read the image, just a good guess.
Correct, Spine does not add new vertices. Exactly how the concave polygon is partitioned into multiple concave polygons depends on details in the algorithm. It shouldn't matter for anything you need to do, it's done only because subsequent steps to do clipping requires convex polygons.
Sounds good!
It may be worth mentioning the one thing people always ask: if they can invert the clipping. No, sorry! It seems like a very similar operation, but actually the math and processing would be more complex to make that happen. With clipping as it is, we only have to clip what is in the draw order between the start and end of the clipping. To invert, we'd have to clip everything.