I'm not really aware of games that don't have realism or consistency (to the extent such apply to fantasy worlds, anyway) as considerations for the GM. Except perhaps exceptions like Toon or the like... where the point is that logic and consistency specifically may not apply.
So, setting aside those common concerns, what else should a GM be considering? In my opinion, they game impact of his decisions. Does this NPC contribute to a dynamic situation in play? Does it simply slow play down? Does it block a player?
I am not saying that there are wrong answers to these questions. I'm saying that I think, in terms of player-driven play, of which I think sandbox play is an example, these questions should be considered. Likely before ones of realism and logic... since we can likely still have a situation make sense. Like... sometimes guards can actually be bribed, or priests do actually take a drink.
To answer that, I think we have to take a step back and ask a more fundamental question: what is the point of the campaign? In other words, what are the creative goals that shape how we run and play the game, especially in player-driven or sandbox-style campaigns?
I would like to hear what you personally think the creative goals are of a campaign focused on player-driven/sandbox style campaign. Then I can reply discussing what else a referee should be considered. I feel the result would clarify things more for you then a discussion about what it is I do alone.
For myself,
My primary creative goal as a referee is to run a campaign where the players feel like they have visited a place as their character and had adventures. Using dice and the mechanics of the game, I aim to create a kind of pen-and-paper virtual reality for the players to explore. Every choice I make as a referee is evaluated with that goal in mind.
The process begins with me working with the players to select an interesting location and situation they’d like to adventure in. Usually, we narrow it down from two or three possibilities. Once that’s decided, I prep the campaign accordingly. Note, I am glossing over the prep part to get to the point where I can answer your questions.
When play begins, I describe the circumstances in which the players find themselves. They then roleplay their actions, and I adjudicate the results, which lead to me describing new circumstances. That cycle repeats itself throughout the campaign.
Let me be clear: NPCs (by which I mean both sentient beings and creatures) are essential to how I run these campaigns. The circumstances I present always include locations and the NPCs who inhabit them. If a player interacts with an NPC, I begin roleplaying that character, sometimes with voices and mannerisms, which I enjoy and perform well. the player responds by roleplaying in first person with me. It is up to them if they want to act, but it is not mandatory. Most players opt to roleplay a version of themselves with one or two quirks or mannerisms.
To manage this dynamic, since I’m just one person and the players are many, I often use a loose round-robin approach. It’s not a formal turn system like in combat, but it does reflect in-game time. For instance, if the party is camped for the night, I’ll go around the table and ask what each character is doing to for the evening, then another go around to handle what happens at night. I’ll typically spend 5–10 minutes roleplaying with each player before moving on. This helps keep the pacing manageable while allowing players to explore their characters and interact with the world. Players often pass if they have nothing particular to do. At times, smaller groups within the party will temporarily form, and I deal with that small group as part of the round-robin.
Regarding your questions:
Does the NPC contribute to a dynamic situation?
Yes, always. NPCs are a major source of dynamic situations in my campaigns. Most interactions, conflicts, and decisions involve them in some way.
Does it simply slow play down?
No. In my experience, these interactions add depth and momentum, rather than dragging things out. That said, pacing is also managed through how I moderate the table, using tools like the round-robin approach I described.
Does it block a player?
That depends on how you define "block." Players in my campaign are never prevented from attempting anything their character could reasonably do (within the limits of good taste). But yes, they can fail, and when they do, they may need to adjust their plans and goals accordingly.
Good questions, however, they don’t exist in a vacuum. Their answers, and their relevance, depend on the overall structure and purpose of the campaign. In a world-in-motion sandbox, NPCs and circumstances aren’t inserted for drama or balance. They’re there as part of the world the players are engaging with. Which is why I asked earlier to about what you think the creative goals are. To better illustrate the impact creative goals on the process.
There are answers to all of these concerns, but they don’t easily lend themselves to short forum posts with clean checklists or fixed procedures. The kind of play I’m describing is rooted in context, continuity, and player interaction with a living world. That takes explanation and actual play experience to grasp fully.