Answer
REMOVE property is used to indicate that a feature or features are going to be uninstalled from the  machine. This property is used as a condition when you do not desire a behavior to occur such as a custom action  to run during repair or modify mode. Hence using REMOVE as the condition eliminates this issue.
REMOVE=ALL  when all features will be uninstalled
REMOVE=Complete  when a specific feature is uninstalled
Note: If you want to list multiple feature, use colons for each feature.
REMOVE=Complete,NewFeature
You can use Installed condition when you want to perform a task during  REMOVE, MODIFY or REPAIR mode.