Everyone contributing to an IT project, ideally needs to be on the team responsible for delivery. When this isn't possible, the more they contribute the closer they need to be to the team.
The above point probably seems obvious to the point of being redundant to most people. I'm sure that many teams (like mine) are structured with a healthy enough mix of skills that they can be mostly self-sufficient. With our team of testers, developers, infrastructure people etc etc I too would have thought we had this base more than covered.
However, beware that contributors to a team's output come in many different guises. I feel that we recently suffered on a project due to a key contributor being very distant from the team.
The project involved adding a new user journey to ft.com. The UX team had designed a user journey, in isolation from the development team, which we were to implement. The user journey that had been created was great, however, the team had another idea which involved less technical effort and might just get us in production (with that crucial real user feedback) sooner.
Thankfully, the product owner, project manager (and I think the UX team) were all open minded in considering the alternative user journey the team proposed. After-all, the original flow could be added later as an enhancement after go-live. The team set off in development with an aim of keeping both options open for a while, but the path of least resistance was clearly the original option and it was up to the team to persuade otherwise.
Sadly, mockups of the alternative flow were never created. I suspect that, as a team, we felt out of place creating them ourselves as none of us wore the UX badge. We could have asked the UX team ourselves but given we didn't know them very well, they sat on a different floor and were outside of technology. I suspect there were too many awkward hurdles for us to overcome. Or, to reference Conway, the "organization's communication structure" did not (easily) allow it.
Eventually a decision had to be made and the original option was chosen. After all, the original option was more "known" to people as it had been presented numerous times with mockups.
As mentioned previously, the original (and chosen) user journey was good and I'm very pleased to say that it's currently live and being used well. But I think we missed a trick by not giving the alternative user journey a fair chance. This would have been more likely to happen had we been closer to the UX team.