Work retreats are a double-edged sword. It's nice to leave your routine and stay in a hotel for a few days instead of going to the office. However, these retreats rarely, if ever, bring about significant change for their attendees.
I've never been on a professional retreat per se, but I did go to a leadership retreat for choir in high school, and it did actually teach me something important. One of the presentations emphasized the importance of listening instead of thinking about what you're going to say next, and that actually changed the way my approach to conversation during my teen years. Maybe retreats aren't so bad after all!
My anecdotal evidence about the positive impact of a retreat is no match for another person's similarly anecdotal horror story about being pressured into going on a workplace retreat, declining, and later finding out the boss made her fellow employees share beds. No amount of vague advice and leadership exercises can make that okay.