>This option enables local file caching, but does not change NFS cache coherency, and does not reduce latencies.

That's true for any NFS setup, not just EFS. The benefit of local NFS caching is to speed up reads of large, immutable files, where latency is relatively negligible. I'm not sure why AWS specifically dissuades users from enabling caching, since it's not like bandwidth to an EFS volume is even in the ballpark of EBS/NVMe bandwidth.