At least one of our inspection templates is for Fagan style reviews, where you have your standard roles of moderator, reader, author, inspector, but additional roles such as observer, auditor, record...
There was a point where it would have been helpful to add another role beyond the fixed set of moderator, etc. - and due to that limitation, another way we tried to tackle this was to use a participant custom field to identify the function / group each participant was representing, however there is also an issue with that as only the participant can change the value of the field. I put in a request to allow the review creator to be able to change the values of participant fields if anyone is interested in that. Using a participant field has the advantage of not needing to specify all the configuration / permissions when they don't need to be different than the standard set, but there could be times when you would want that level of flexibility.