At home servers are extra space and electricity, AND potential outages if your ISP isn't 100% stable. I had outages sporadically for 2 weeks because a squirrel chewed through some coax outside my house. Im glad I didn't sporadically bounce emails for 2 weeks during that time. I'm sure a major provider has redundancy and controls in place for failovers... a single server in your house probably doesn't.
