This determines if Inno Setup's automatic uninstaller is to be included in the installation. If this is yes or to a boolean expression evaluating to True the uninstaller is included. Otherwise, no uninstallation support is included, requiring the end-user to manually remove the files pertaining to your application.
Setting this to a boolean expression can be useful if you want to offer the user a 'portable mode' option.
[Setup] Uninstallable=not IsTaskSelected('portablemode') [Tasks] Name: portablemode; Description: "Portable Mode"