Hi mir4ea,

> Thanx Michael, now I can understand what this command do) And yes it could be useful especially
> when the underlying surfaces is big to reduce its size. Or may be there is the other point to use it?

Well it can help reduce file size if you have only small remaining pieces cut out from much larger and complex original surfaces.

Sometimes it can also help avoid problems in complex operations like offsetting since it has a kind of simplifying effect. If you have surfaces that are self intersecting or bunched together awkwardly but those bad areas are outside of the active trimmed area then this command can get rid of those bad areas of the surface.

So sometimes if you're having a problem with complex operations it can be worth a try to run it to see if the shrunken down surfaces behave better with that particular operation. But after you do it, it's not so easy to restore the full original surface later on by untrimming though, so you it's not something that you would just do all the time automatically.

- Michael