I'm a governor at a secondary in a large MAT. That we're volunteers doesn't mean much and the only time I've had it brought up is in training to remind us of the limits of our role.
How valuable we can be depends on a lot of factors - our own perspective, training, and ability to remain strategic, the composition of the LGB, the HT, clerk, Chair, in a MAT it can depend a lot on the CEO and scheme of delegation & how the school improvement officers view things, and more. I think we have to proactively be of value, it doesn't come with the role, but even those who are proactive in any of the roles can be stopped from doing so by other parts of the system.
If you're stuck with someone in a position of authority (including other governors) who just wants yes-people or to get through the tick list, if the composition of the board or SLT or trust school improvement officers are largely people from similar backgrounds with similar perspectives, if you're focused on the how they're 'nice people' or on how governors are 'giving our time voluntarily' (technically everyone should be, no one should be forced to be there, some are just getting some financial compensation), or other barriers to strategic scrutiny, we can be just a tick box exercise that eats into time for the real work. It's very easy to be a warm body in a chair tick boxer as a governor, especially if you have a trust that prefers their LGBs that way.
For the specific issue on the school office - I've never waited or even been in the school office. It may be helpful for the staff and for the governors to discuss alternatives. I always ask for a place to meet if I'm meeting a staff member as I know reception can get crowded - usually If I arrive before the meeting room or staff member I'm there to see is available, it's agreed to wait in the LRC unless it's being used for a lesson (a couple of my linked area involve the LRC, so it fits well to start there). On a few occasions, I've been asked to wait in the staff room or outside a particular toom. Sometimes when possible governors will meet up outside to talk before going in.