What is the mgc.pkginfo file?
The mgc.pkginfo file contains the cross-reference information which describes what "atomic" licenses are included in "composite" features.
When does it need to be updated?
The mgc.pkginfo file needs to be updated when product bundling changes in a new release, and you want to use the new license in an older version of software.
Let me look at a example as a way to describe this in more detail:
Last year, Expedition introduced a "dual" license which enables either Design Capture or DxDesigner to be run. The new license is called "wgdxd_c".
This "wgdxd_c" composite contains both "wgdsncap" (for Design Capture) and "viewdraw" (for DxDesigner). The composite license "wgdxd_c" is then checked out when either tool requests a license.
The latest release of software already knows about this new license (because the mgc.pkginfo file supplied with that release contains the information) but what about older software releases?
If you want to use the new "wgdxd_c" license with older releases of software, you will need to update your old software tree with a new version of mgc.pkginfo.
How do I update mgc.pkginfo?
Technote MG504224 contains an automated method of updating the file, and a link to the latest file along with a manual method (if you prefer that method).