Comparisons & alternatives · macOS's own storage tools
Is Offload in Storage Studio like the iPhone's Offload Unused Apps?
Short answer: Similar idea. iPhone offloading removes the app but keeps its data on the phone; Storage Studio's Offload archives the app and its data onto your external drive and restores it exactly, with no re-download.
Similar idea, different destination. On an iPhone, offloading removes the app but keeps its documents and data on the phone, and the app is downloaded again from the App Store when you tap it.
Storage Studio's Offload, in the Apps window, archives the app and its data onto your external drive and removes both from the built-in drive — so it frees more space than the iPhone version. Nothing is downloaded again: Restore, from the Offloaded tab, copies it back exactly as it was. The app can't run while it's offloaded, and restoring needs the external drive connected.
Everything is copied and checked before the originals are removed, so an offload is never left half-done. If you'd rather keep using the app day to day, Move it instead — it runs from the drive with a link left in Applications. See Apps.