Many online communities have multiple screens or experiences, such as a Q&A site, a chat room, and possibly a blog with comments. An example is what SE calls "third space", like chat. What are the pros and cons of having same people vs. different people moderating different faces of the community?
I run a gaming community that is split across multiple different "fronts". We have forums and we have game servers. The game servers are split between the few games the community sponsors and in a couple of those games we have a further split between "serious" and "fun". Each of these areas have aspects of moderation.
On the forums, there are two levels of moderators - community administrators and moderators. These two levels are here to keep the peace. The few administrators are the "voice of god" when official announcements are made and when community wide events need to be dealt with. The moderators are "in the trenches" and handle many of the day to day activities on the forums. They deal with user complaints (and compliments), handle suspensions (and unsuspensions) and the occasional bruised ego. The way the forums are set up, each could handle anything, anywhere, on the forums but the moderation team has decided to divvy most of it up to cover their respective game areas. They overlap only in the dedicated "suspension appeals" area and the "general chat".
From an administrator point of view, this seems to be working out. In the game specific discussions, the users know the moderators. In the general chat, the community can interact with the entire team of moderators. This is nice because many users don't hop between games that often, so they don't know "the other side of the fence" moderation teams as well. In the suspension appeals area, the overlap is nice because neutral third party moderators can weigh in.
On the servers, we have moderators by game type and local moderators. The game type moderators have permissions across all game servers of specific games to handle any complaints. These moderators can jump between servers can deal with problems as they crop up. A few of our less frequented servers also have local moderation users. These users have the ability to deal with problem plays only on that specific server.
Initially, we didn't have the local moderation teams, but as we grew we found that we couldn't cover a whole 24 hour time period of moderators for all servers. Instead of adding more global moderators, we went with more local moderation. This provided us with users that understood the culture of the server - "fun" vs. "serious" - and the usual players.
Each game server moderator receives moderation abilities on the forums too.
The way the community is set up has worked for us very well. Once a month, the community administrators pull the moderators into a "town hall" type chat where we can take the pulse of the community. As we are set up, we have several sub-communities and each have slightly different concerns. The moderation teams use this chat as a way to relay concerns further up the chain and to talk to one another. While the moderators of the same game talk frequently, communication across games is less common, and this is a chance to open that path of discussion.
From my point of view, I see several pros and a few cons to this set up. On the positive side, I have multiple moderation teams that are invested in how their sub-community operates. They want it to be successful and they want to grow. The moderators know a larger community exists, but they can focus on their narrow area of influence to better how it operates. Several of the game servers have implemented their own policies on how strict (or lenient) to be. The moderators advocate for their users and because of that we have launched new servers for users - a "kid friendly" Minecraft server, an "adult" server where users don't need to be as careful about language they use, etc.
The regular cross site meetings are important too. The moderation teams can learn from one another and see how different games handle different problems. It allows the administration team to quickly get the pulse of the community as a whole and see if their are developing problems that affect the entire community.
On the negative side, there have been instances where a moderator that isn't involved in suspension adds their opinion to a problem that is unhelpful. With several game servers having different sub-sets of rules, there are bound to be times where a moderator doesn't know local policy. It happens, and the solution we've found is the explain (usually publicly, because that's where the discussion started) the policy that is unique to the server. The moderator that spoke up may feel a bit embarrassed, but the correction does two things: educates the moderator about the differences (this is good) and allows the discussion to move forward instead of focusing on why action on one server is good but on another is bad. Those types of discussions can be held independent of the suspension discussion.
Overall, I am happy with the varied moderator teams. The locality helps to build the sense of community for areas of the community. The global aspect in areas of the forums helps the community cross pollinate and see how different areas interact.
So this is one of those annoying cases where the answer really is "it depends". Some of what it depends on can include the following:
1. How much traffic each community face gets: if your community is busy, you'll need a bigger staff of moderators.
2. What the bandwidth of your community leaders is: similarly - the more tasks: reviews, requests, spam, and engagement your community leaders have to approve, edit, or referee per face, the more likely you'll need to specialize.
3. What the availability of your community leaders is: the difference between bandwidth and availability is who can staff what hours or days and respond to issues in a timely fashion. Some community faces need more constant attention, like a chat room or online game.
4. How different the audiences and subject matters are: if a certain face has a lot of new members, for example it needs a different kind of appraoch than where the more experienced members hang out. Similarly, if there's an expectation for a certain amount of expertise in certain forums, then you may need specialized moderators.
5. What your moderators like to do: you will find certain moderators like doing certain kinds of tasks more than others. Maybe they love answering difficult questions. Maybe they love interactive chat. Maybe they just love meta discussions. Why deny a dedicated specialist by forcing them to cover other faces that don't appeal to them.