When I worked at PNC Bank, they flew me out to Boston to conduct user research to start exploration for a redesign they needed on a newer product they had acquired, a SAaS tool used for wealth investments. This was a shell service, and anything I designed needed custom branding that could be scaled for their bigger clients like BlackRock, Vanguard and Charles Schwab.
They had internal users who used the product to build portfolios for clients, as well as client companies who used the product to do the same for their own clients. Users themselves also could use the product for self-service.
This unique structure called for unique user research. We had to understand that some of the key stakeholders were also users, but they weren't the only users. Each demographic needed it's own persona, and its own problem statements and user criterion.
GIS was using a unique internal technology at the time that allowed us to quickly prototype the designs, and use the styles as skins that were interchangeable for their clients. This meant we were able to do user testing with the client's real actual data, making it feel more real and personal to them. That had an emotionally charging effect to their feedback; any positivity was appreciated in a heartfelt manner, while negative feedback came quick and sharp.
Those results gave us more confidence in its certainty. We knew exactly what we could or couldn't accomplish, which unlocked new goals and product direction they were either unaware of, or didn't image was possible in a small timeframe.