A bit of background: I attend University A. I have done all of my studying so far at University A. I completed my undergraduate degree in Faculty 1, I will complete my masters in Faculty 2, and I am considering applying to do a masters (track to PhD) in Faculty 3 to study a new field. (I can clarify the field jumping if needed, but not sure if it's necessary)
I understand that if somebody started out in chemistry, for example, that doing an undergraduate, masters, and a PhD at the same institution could have some career downsides (smaller network, access to the same resources, etc). In this case, it seems clear to me that there is an added benefit of doing a PhD at another institution.
In my case, however, I have been in multiple faculties within the same institution. If I were to apply and do a masters/PhD in a different faculty at my university (University A) then it's not as clear to me what the potential downsides would be for an academic career after the PhD.
So I am curious what the opportunity cost of pursuing a new field at the same institution is, and ultimately, having finished ones entire academic career at one institution.