Sometime a feature has an unacceptable set/combination of attributes, which means that the feature must be stopped from being output normally. If this is detected in AttributeManager, e.g. in a conditional value, there's no mechanism to block the feature. It has to be done using Testers before or after.
If a "rejected" value could be set, and the action could be expanded to react on such a rejected value (or do it automatically) by either terminating the feature or outputting it via another port (e.g. <Rejected>), it would simplify the overall logic and minimize the clutter of transformers.
Cheers