This feature suggests, to group different projects in Customer portal, to make it easier for customers to find what they need. i.e. If an instance has IT requests and non-IT requests then based on Request types we can group them in Customer portal. In such case there would be 2 portal groups and 100 request types for eg.

However, if we have a feasibility to group them by the projects then we could just have the project groups listed in Customer portal and then we should be able to drill down the request types under each group.