This activity gets students in an active frame of mind at the start of section.  If section meets a long time from the last lecture (say, for a Tuesday-Thursday lecture schedule, the relevant section meets on successive Mondays), the instructor can get students into gear by taking the first few minutes of section and having them to jot down 2 or 3 topics or themes that were of interest from the previous week's lectures.  (Of course, this can be useful even if section follows right on the heels of lecture.)  This gives students time to look over their notes, if necessary.  (It might also be helpful to have them pair up with a nearby partner, if the material is especially challenging, in the manner of a think-pair-share exercise.)  Once a couple of minutes are up, the instructor starts populating the blackboard with general remarks, which then forms the basis of the more standard discussion to follow.