There are no viruses in the wild that affect Macs. That might change, but if/when it does, the entire world will react and you'll hear about it. In the meantime, as has been said, all that any AV package can find are Windows viruses that will not affect your Mac in any way.
Most of what the AV packages find are viruses in emails which originated or came through a Windows system and picked it up. About the only justification for running it is to prevent you then forwarding it to someone else if you forward the email. But then, they should have AV software themselves, so it's really up to them to protect themselves.
One last thought. All AV packages protect on known viruses and known vectors of attack to block any new attempts in that vector. There are at this time no known vectors to attack a Mac. So there is nothing the AV can even check on as it sits there. That makes it doubly useless. It has nothing known to check for and no known vectors to monitor. Basically, it's useless.