to summarize or not to summarize…

Since the reading of Jeanne Desy, where she speaks to the practice of having her students write summaries until they become good at it, I have been considering doing the same thing in my class.  That was until last week when L Lennie Irvin advised against it.  What are your thoughts?  Do you think summarizing can be a useful tool to help transition basic writers into the realm of academic writing or is it an ineffective time waster?