Mac storage basics · Apps and macOS itself
What is the Application Support folder, and why is it so big?
Short answer: It holds apps' working data — databases, downloads, plug-ins — often the only copy. Remove folders of uninstalled apps and use apps' own settings to clear caches.
~/Library/Application Support is where apps keep their working data: databases, downloaded content, offline files, plug-ins and sometimes caches. Chat apps, editors, music software and browsers can each keep many gigabytes here.
Unlike Caches, this folder often holds the only copy of an app's data, so don't empty it. Look for folders of apps you've uninstalled, and use each app's own settings to clear its cache or downloads. Storage Studio's What's Using Space names the app behind big folders here when it can, and says when it can't tell.