It's pretty useful when making phishing pages. Rather than having to host all the tiny files and images yourself or going through what is likely an enormous HTM

It's pretty useful when making phishing pages. Rather than having to host all the tiny files and images yourself or going through what is likely an enormous HTML file and editing all the srces and hrefs, you can just throw a <base> tag on there and be done with it. Admittedly this is probably not the use case you're looking for.