Gotcha. So, if I set it to do this automatically, then both programs could stay in sync. I can check out if there's a performance hit significant to bother me.
And would I be correct in assuming that once LR has made changes and stored them in the catalog and also written to the sidecar file, if I tinker with the file in ACR again, those changes would get picked up by LR the next time I open it there? Or would it revert to the catalog settings? I can just try for myself tonight and find out, but maybe you know?