My impression is that its invention was for the sole purpose of eradicating the idea that Windows is insecure and prone to viruses, which explains why it can be overzealous and CPU hungry.
I would only enable it for family members who don't know what they are doing. For some reason, I haven't needed any form of active virus scanning in something like 15 years. If it turns out I've been infected this entire time, the criminals sure are taking their time stealing my money, etc.
I think this would describe the majority of computer users. And the majority of computer users are also using Windows.
> I haven't needed any form of active virus scanning in something like 15 years
Microsoft Defender antivirus was released alongside Windows 8 in 2012. And it's essentially a rewrite of Microsoft Security Essentials which came included starting with Vista. If you haven't been explicitly disabling it, which your comment sounds like, you've been running one without knowing it for 16 years