The goal in staffing, I think, is to provide area expertise, big picture understanding, and historical context, for each position you need to fill.
The question comes from when you're short on one of those, and how to make up for it.
A good generalist can often fake it on area expertise.
Knowing or being able to influence the inclinations of candidates for the position can help you select someone who will tend to act in accordance with the big picture without necessarily understanding it.
Good documentation can help fill in historical context.
Teams of people can hold these qualities collectively.
Right now at work I feel like I'm a generalist who was selected for his process inclinations and handed a big pile of documentation. Eventually this will translate into expertise, understanding, and context, but in the meantime it's a little unnerving. I wonder if the folks I gave level-skipping promotions to in Arisia felt the same way?