WOFF2 cannot be installed on most computers and old browsers do not support it. WOFF loads on every browser as a web font. WOFF2 is at home in fonts on web pages; WOFF is the usual choice for fonts on web pages, as a fallback for WOFF2.
The outlines and tables of the font are copied unchanged and only the wrapper around them changes, so the letterforms, hinting and layout features are exactly the same. WOFF2 is handled by a WebAssembly module that downloads the first time you open WOFF2 and is cached; the font is expanded back to plain tables. WOFF compresses each table with zlib, so the file is smaller than the TTF or OTF it came from. A file that is not a TrueType, OpenType, WOFF, WOFF2 or collection font is refused.