Explain purpose of FreeNAS/VM Running ESXi?

My buddy that originally got me into building etherium mining systems is now raving about some server and personal cloud thing he built. I just dont understand the purpose or why the average guy would find any utility in a home network etc worth building a new computer just for networking purposes (just like a big high tech hard drive)? Can someone enlightening me why this stuff is advantageous and give me some examples of how this could be used to make my life better in any way?