Comparisons & alternatives · macOS's own storage tools
Why not just turn on macOS's Optimise Storage instead of using Storage Studio?
Short answer: macOS optimise storage keeps files in iCloud and leaves placeholders on your Mac. Storage Studio moves big folders and apps to your own external drive, complete and at full speed, with no iCloud plan needed. They work well together.
Turn it on if it suits you — but it solves a different problem. macOS's optimise options lean on the cloud: files and photos are kept in iCloud and only small versions or placeholders stay on your Mac, and watched TV shows and films can be removed. That needs enough iCloud space and an internet connection whenever you want the full file back.
Storage Studio moves things to an external drive you own instead. The files stay complete and open at full speed while the drive is connected, with no upload and no iCloud plan needed. It also handles things optimise storage never touches — large app data, developer caches, virtual machines, and the apps themselves.
Many people use both: iCloud optimisation for photos and documents, Storage Studio for the large, local-only folders. See iCloud & iCloud Photos for how the two fit together.