The concept is simple: the original game files are compressed using advanced algorithms to significantly reduce the download size. For a game like Days Gone , a repack can compress the game from ~70GB down to roughly depending on the specific version and selective downloads (like language packs).
The Days Gone PC port is famously well-optimized. Even the version retains all the graphical fidelity of the original release. Players can enjoy: days gone fitgirl repack days gone highly c portable