Hi Friend,
I deal with SDRS in day to day job.
I suggest you to enable SDRS on the datastore cluster as your file server may have several disks. (In future you would be adding more disk as well)
I also suggest you enable SDRS both for space & IO balancing. SDRS will place all the disks automatically on appropriate datastores & balance from space as well IO perspective. Also when you enable, IO metric on SDRS cluster, it enables SIOC on each datastore in a datastore cluster & it will help you to throttle the host IO queue depth in case of IO contention, which is going to improve IO performance.
File server would be IO as well as space intensive. Hence SDRS is going help you lot.
let me know if you have any other query.