Every user's app data lives in ~/Library, hidden by default. Inside it:
| On Windows | On a Mac |
|---|---|
%APPDATA% (Roaming) | ~/Library/Application Support |
| Registry settings for an app | ~/Library/Preferences/com.maker.app.plist |
%LOCALAPPDATA%\Temp, caches | ~/Library/Caches |
| Event logs | ~/Library/Logs, and the Console app |
%PROGRAMDATA% | /Library (for all users) |
To open it once: hold ⌥, open Finder's Go menu, and Library appears in the list. To keep it visible: open your home folder, press ⌘J for the view options, and tick Show Library Folder.
Deleting an app leaves its Application Support, Preferences and Caches behind, usually a few megabytes. Safe to delete after the app is gone, except for anything you want to keep, such as a mail client's local mailboxes.