Cool deal: 27" iMac 5K with 1TB Fusion / 24GB mem / Applecare only $1655
File Sharing and Remote Access
Turn OFF everything you don’t use.
There is simply no reason to needlessly invite trouble by enabling services you don’t use (though Mac security is excellent, tempting fate is not a good idea).
I use File Sharing between my Macs, so I leave it enabled.