Similarly, my advice to participate in study groups carefully is due to the frequent disfunction that can occur in them. Some students dominate the discussion; others are not prepared and instead hope to "free ride". So spending a lot of time in a study group that does not have a plan and ground rules can be a waste of time.
However, there is huge benefit to be gained from cosulting your colleagues in law school. This is because there is no substitute for the synergy of creative thinking that goes on among law students. Simply, two (or three or four) heads are better than one. And in law practice, I have found that while treatises have their place, there is no substitue with kicking legal doctrine around with your colleagues. The practice of law is a craft, perfected by craftsmen (or women). And the art of the craft is the winnowing and distilling of ideas and doctrine through consultation with one's peers.
And in law school, smart and creative people are all around you. Seek them out. Bounce ideas off of them. Check your thinking. And the advantage of doing it ad hoc and on your on is that you can control the schedule and timing of this consultation. In a study group, you are often constrained by the activities of the group itself.
So, when I caution against engagement in study groups, please do not consider this as a prohibition. Instead, think of it like you would in the same way that you would all of your study activities- an investment of time. Engage in that free-form creative analysis unique to law school on your terms, with people who are willing to work with you in a collegial way. Don't simply succumb to a study group because everyone else is.