Create Derived Substitute

[simonmunyua6]

what is the importance of this command on the inventor?

[A.Acheson]

Deriving a part allows a linked copy of a part where the core geometry will remain linked but the iproperties can be changed.Think of generic part then derived multiple parts where the vendor, part number, stocking location information is changed. One part will control the geometry of several others allowing quick updates to be performed.

Deriving a multibody part allows for removal of bodies such as internal bodies for either file size reduction or removal for protection of intellectual properties. 

Deriving  of an Assembly to a part allows for  semi linked(manual update) of  core geometries. Where design views, parts etc can be changed.  Great for file size reduction in large assemblies. 

The down side is the BOM information cannot be used later as the bom information will only be shown as a part file. 

Here is a link to the help page. And here is a link to a video showing its use. 

[Gabriel_Watson]

It combines three tools into one: Derive + Replace + Substitute.
I find it useful mostly for simplifying larger assemblies so you can hack and slash at the alternate Model State "Substitute", and save what changes you might need during a design review, for example. You can also use this as a form of "freezing" a copy of some assembly at the time, to use it in presentations and manuals, without worrying about the original files.