[ck2]

I don't think you follow that with a local file system, file stat (basically to see if the timestamp has changed or file modified) can be done directly inside the local memory cache.

On NFS/NAS it cannot be done locally, because other devices may have had access to the remote filesystem and changed files. So it has to travel the network to make the query. Even if it doesn't have to touch the disk remotely and can fetch it from a remote cache, it's significantly slower than local. Even if it's only 1ms per file, if there are 300 files, that's 300ms (a third of a second) on the SERVER side, before it can start sending output to the internet.