In comparison with traditional font formats like TTF or OTF, they provide better compression while keeping a lot of features of those formats, like ligatures, small caps, or alternative styles. Those feature can be used in CSS by leveraging the
font-feature-settings property. WOFF2 provides even better compression and faster decompression, which is especially important on mobile devices.
WOFF is available in all modern browsers. The only notable exceptions for support are IE8 (and previous versions, obviously), Opera 12 & Mini, and Android Browser up to 4.3. The enhanced WOFF2 is available in Firefox 39+, Chrome 36+, modern Opera, current Android Browser and current Chrome for Android. (See CanIUse.com)
By using the modern file formats and providing a good fallback font for browsers not supporting WOFF/2, websites render more quickly, the build process is quicker and more easily to maintain, and users with older hardware don’t get the additional burden of downloading and decompressing a font file.