With start date and / or duration it would be possible to give the responsible an idea of the time frame a task must be completed. With due dates only this isn't possible.
A predecessor task could help to calculate end dates of a several tasks. This is not ment as a project management solution - just for helping users to structure their daily work.
Activity templates are a good thing, but if someone has to manually add due dates the value is reduced. With the mentioned requirements such templates will be more valueable for users.