What is the role of tile-system in a game like Project Zomboid?

I understood the purpose of a tile system to be either for traditional board-game style games, or because it's an efficient way to handle procedural generation worlds.

In a game like Project Zomboid where player and AI movement does not appear restricted by tiles, and the map is not procedural, what purpose does a tile world serve? Could it be for more efficient AI path-finding? I.e. rather than build a navmesh we just sample array of tiles to get type available for movement? Or helps with performance in loading/unloading?

 

I'd guess yes to both. Implementing a grid-based A* pathfinder is simpler than an irregular navmesh. And it certainly make it easier to identify boundaries for streaming bits of the map in and out.

In addition, it might have made it easier for the devs to create the maps, using something like Tiled for example.

 

^^^^
This