Most experienced interface designers have been in the position of working on projects that include representatives from multiple business units. In the worst case scenario, each representative advocates strongly on behalf of his or her own business unit, trying to optimize the design to the business unit's advantage. If the designer doesn't have the explicit support of the project manager and other stakeholders and loses control of the design, the interface design specification can become a sort of battleground for the competing interests of the BU representatives. Design decisions are made on the basis of political power rather than on good design principles; the interface design and the designer both suffer. "Design by committee" is the perjorative term given to the unwieldy output of such exercises.
A few companies ignore the negative connotation of designing in groups and practice design by team. Those who do include designers, engineers, and user researchers on the team. To get this to work right, the participants must be both designers and committed team players who can subordinate their own egos for the good of the team. Two very different, and somewhat rare, skill sets. Teams take time to function together at a very high level, so the successful team would have had to go through a period of getting to know each other's style.
It's an interesting approach, and I'd love to study design teams over time, and find out what works and what doesn't. Teams and design, what could be better.