The shared volume is there as a value add you can get away without it. In a typical “uploads are on AWS”, PG / Redis somewhere central setup you will only use it for Rails/Unicorn/NGINX etc logs. You would then ship them somewhere central with some log aggregation service.
Just wanted to check that there weren’t going to be issues with uploads going to one host, and then a request hits another host and isn’t available due to it running in a separate container with a separate mount.