According to SAP note 3053335, workflow rule actions that are scheduled “OnSave” are executed BEFORE the BeforeSave. Accordingly, the BeforeSave cannot influence the OnSave action.
However, SAP can enable a backend flag, called “Late Condition Evaluation”.
With that enabled, OnSave actions are executed AFTER the BeforeSave and therefore the BeforeSave suddenly has an influence on the OnSave action.
In addition, an OnSave action always invalidates the associated BO (regardless of whether the action changes anything or not), i.e. BeforeSave is executed again .
Without “Late Condition Evaluation” this has no effect, as the BeforeSave comes after the workflow action anyway.
With “Late Condition Evaluation”, this leads to an additional BeforeSave (BeforeSave => Onsave Action => BeforeSave).