Today, if you have a top level project (but you do not assign any group to the list of permitted groups), then creating a child project beneath (and thus do not inherit permissions from the top level project) and assign one or more groups to the list of permitted groups, then as a member of one of the groups that is permitted to access the child project, the child project cannot be viewed.
In such situation you get the error “MKS 124814: Cannot show view information: MKS 124283: Permission Denied: Item xxxx is not visible due to project/type visibility restrictions.”
By allowing parent inheritance, it would help setting default access permissions across all the child projects, and then only have to add permission explicitly to each child as needed.
This would in most environments be a more efficient and faster way to assign permission across child projects.
This is a missing functionality on the IM-side, based as seen in Article https://www.ptc.com/en/support/article?n=CS168424 along with a confusing setting on the child project permissions as in Article https://www.ptc.com/en/support/article?n=CS170094.
