First of all, the big difference is that "Unassigned Lessons" won't impact your "Acceptance Rate". You are by no means obligated to pick up an Unassigned Lesson, however we do encourage it! These are lessons that were once booked with another tutor who then cancelled, so these students are actively looking for a new tutor for that time slot.
As such, these are great lessons to pick up for some quick cash, or to meet some new students. Similarly, you can pick up these lessons on very short notice, so if your afternoon suddenly frees up and you fancy earning some money, you can do so with these!
As a final perk, if you pick up an Unassigned Lesson or your lesson is reassigned within 24 hours of its scheduled start time, you will be guaranteed a rating of 4.5/5 for that lesson, to acknowledge the fact that you may not have had as much time to prepare for this session or the student as with a normal lesson!