There's already a nice selection of free antivirus programs available for the discerning user, but it's hard to say no to a new entry. Sophos already has a free product available on OS X and it's recently dipped its toes into Windows' waters.
The question is, is it worth using over something like Avira or Avast? According to gHacks Martin Brinkmann, that all depends on how much control you like to have over your AV software. I'm feeling confident the answer that is "a lot".
Unfortunately, it appears Sophos Home requires you to use an online dashboard to configure it, once you get past the "cumbersome" installation that needs a Sophos account. It also installs a fair chunk of services too -- eight in total.
If you don't mind these caveats, Sophos has a good track record in terms of actual protection, so at the very least you'll be well protected.