Upgrading from an old version to a "renpy repack new" version can sometimes break save files if the internal persistent data structure has changed. Always back up your /game/saves folder before migrating. The Future of Ren’Py Distribution
Many new repacks convert heavy PNGs to WebP format. renpy repack new
New repacks often allow for "delta updates" to save bandwidth. Why Players Seek New Repacks Upgrading from an old version to a "renpy