If you're referring to user groups, nothing has changed in version 5, but you can have as many groups as you want in v4 as well. The built-in ones are just special since they don't depend on the user.
In general, version 5 mostly has a technology advantage over v4, in that it has updated its architecture from MVC to REST and dropped unmaintained libraries such as Stripes and Hibernate 4, in favor of more modern and actively developed libraries such as Angular and Hibernate 5. We've added the Spring framework to wire services up instead of using the simplistic in-house solution we had in v4. In general, our aim is for Portofino 5 to be more modern, more developer-friendly, and better suited to a microservices architecture.
However, from a user's point of view, it's mostly a matter of aesthetic preference. Not everybody likes the Google Material UI that comes with Angular. On the other hand, Portofino 5 makes it much easier to develop a custom UI using other technologies. E.g. with React you can use
https://www.npmjs.com/package/portofino-react-admin