browserconfig.xml was introduced in Internet Explorer 11 and lets you define advanced web application tiles. Most of its features are too advanced for web applications that do not target Windows 8 platform capabilities. However, browserconfig.xml is very useful when it comes to favicon: it defines the various tile pictures and background color.
In fact, browserconfig.xml is not necessary. Tiles can be described directly from the HTML code. But the extra XML file has a sensible advantage: unlike HTML pages, it is loaded only by Windows 8 devices. And since most visitors do not use the Windows 8 + IE11 combo, we are glad not to clutter them with useless stuff.
By default, IE11 looks for browserconfig.xml at the root of the web site. RealFaviconGenerator takes advantage of this characteristic. Since a few months, when you choose to place the favicon's files in the root directory, the XML file is generated. Yet, as Giuseppe Caruso pointed out, the location of this file can be overridden with the help of a <meta> tag. RealFaviconGenerator now uses this markup to rely on browserconfig.xml whatever its location. That was issue 32.
The gain? A few hundred of bytes. Nothing fancy, just the kind of little improvement that makes the service better, day after day.