Can't share on network unless SMB is unticked

Got a brand new iMac and have been having connection issues on my home network. Other network Macs cannot connect to the new iMac. After much searching, discovered online that by unticking SMB as a connection option in Sharing prefs, Options, it solved the problem and I can connect to the iMac now. Problem is, when I restart it then resets that setting. Also, I am not sure if not being able to connect by SMB is compromising network performance or not. I really don't know what it means to not connect by SMB and so only use AFP for sharing. Any clues or advice about why this is happening and what it means to my network usability?