You can invite a user into the app more than once into a different role.In terms of their permissions they will get the most permissions possible based on all the rules they are in. But of course they cannot get the most dashboards possible or the most different user interfaces possible.
The way the system decides which dashboard to Lanza user on or which user interface tables to Sherwyn Hyde is based on which role is highest up on the list of rules. So you will need to go to your list of rules and drag and drop them into an appropriate sequence. So typically the rolls with more permission should be drank up higher on the list. (This was dictated in the sunshine on an iPhone so I hope it reads OK.)