My short story is related to this topic.
When some years ago i caught my dad browsing through pron sites (of course i was shocked at first and closed session immediately) while i was connecting with Teamviewer to do remote PC maintenance cleaning, i realised something has to be changed (not the fact it self) but PC security wise, because all security software on Windows 7, 6 years back then on Dads PC was just at deffault settings with WD on, and he wasn't really aware of the coincidences which may happen of "brain-dead" link/image/advertisement click.
I believe in these days we live in, there is a very high chanse of getting an infection on windows systems, there MUST be someone in your family/friends who could take care of your PC or atleast is familiar with cleaning it/removing malware/creating backups, because my parents for example don't care about all this stuff, and just want Windows to work as they would want from the moment when installed without installing any additional software or configuring Windows settings for specific kind of needs, work/multimedia so on.
M$ has improved Windows Defender with Anniversary Update, so its great step forward of using just in-built Windows security. I'd say paying for an AV as home-basic-user is NOT a waste of money, but for advanced user it is, because you can secure your PC with just in-built Windows tools and common sense. If we talking about additional security software for windows, its worth investment ONLY if you know what you are doing and for what kind of purposes you need it for.