WOFF cannot be installed on most computers, and WOFF2 is smaller. WOFF2 is the smallest web font format that browsers support. WOFF is at home in fonts on web pages, as a fallback for WOFF2; WOFF2 is the usual choice for fonts on web pages.
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 compress to WOFF2 and is cached; WOFF2 reorganises the outline tables, so converting back gives the same glyphs but not an identical file. A file that is not a TrueType, OpenType, WOFF, WOFF2 or collection font is refused.