I think a good rule of thumb is that anything I want students to learn should be:
- introduced as early as possible
- seen constantly, and better still used constantly
- made as easy as possible for students to learn from me, by following instructions and also by observing my regular example.
Leaving such things merely "suggested" or "optional", though it seems to grant freedom, is equivalent to not assigning them at all. Rather than the community of excellence that I hope for in my heart, I usually end up with a slum of underachievement, instead. Generally, only a really superior student ever does "suggested" activities, and even s/he rarely does many of them.