Recommended tasks pop up when the student hits the Start button and there are no tasks assigned by their teacher. So, if the teacher has no yet assigned any work or the students has already completed all of their work, recommended tasks will pop up.
Mathspace will go through and make suggestions for the students to work on subtopics based on previous work they have been completed. This is an alternative to the student selecting the "No thanks, I'll choose my own" and being directed to the Topics page where they can work on something. The idea behind this, is that students will always have something to continue on with, even if the teachers hasn't assigned anything to them.