There are pros and cons for using internal resources to conduct the investigation or appeal, and likewise, there are pros and cons for going external.
There is a cost factor with external which you don’t have with internal. However, busy managers and leaders may bring high value to the business by executing and delivering on their key objectives rather than being tied up in internal investigations or appeals.
The secondary downside of using internal resource is that the process may longer than an external third party as the busy manager is trying to get his/her ‘day job’ done as well as slotting this investigation into their busy schedule.
However, in going external, you want to be sure to choose a third party who will deliver quickly, and not let the process drag on for an unreasonable period of time.
The key benefit of an external party is their independence in the process. They should have no conflict of interest in conducting the investigation or appeal. The report of external investigators may carry greater weight in the WRC or in a court of law. There may be a perception, rightly or wrongly, that an internal investigation or appeal is biased or subjective in some way, and this may lead to further issues for the organisation.
A further factor is the separation of the roles in what may be a lengthy process. For example, if there has been in internal investigation into fraud, which led to a disciplinary process, which was conducted by internal parties, the outcome of which was dismissal and this was appealed. In this case, it would be best to have the appeal heard by an external independent person(s).