Anywhere where you need local integration that is tighter (or easier) than what you'll get on [preferred web platform].
E.g. for a Windows app: reading files, connecting to Outlook, adding things to the registry, Windows Explorer context menu support, draw stuff on the desktop, plugin for Visual Studio, easier task-tray integration, better global shortcut key support, Win32 API trickery if you need to make controls do what they don't currently do.
E.g. for a Windows app: reading files, connecting to Outlook, adding things to the registry, Windows Explorer context menu support, draw stuff on the desktop, plugin for Visual Studio, easier task-tray integration, better global shortcut key support, Win32 API trickery if you need to make controls do what they don't currently do.