Most people simply have a liquid protein drink. This is not enough as after a heavy lifting session you need to restore glycogen in the muscles as soon as possible, this is best achieved with liquid carbs, simple sugars, and the best is dextrose monohydrate as it has the highest glycemic index of all simple sugars.
So instead od instructing lifters to simply have a protein drink, the post workout drink needs to more than that. Around a 50/50 split of carbs and protein