"But wait Mary Beth (you might be saying), knowing how to work in a group is an essential skill everyone needs once they enter the work force. If you can't work as a team, many times things cannot get done or run smoothly."
You make a very valid point, there is a huge benefit to be gleaned from working with other people. However, lets use the second word that you chose ... TEAM. A "group" is a number of people coming together in close proximity to become classed together. A "team" is a group of people coming together for a common goal. So the idea of group work is a valid one, however it is quite often poorly executed. For example, a teacher says "okay class, we are going to be researching how animal life works and the different systems that can be found within the different life forms. I want you to get into groups and fill out this worksheet."... and that's it. Typically what will happen is one person will either elect or be relegated to the role of leader and they are then tasked with doing most of the work in the group.
So instead of having a group of students do "group work", here they are actively using their own knowledge and then building that knowledge off of other players. They have specific "cards" in their hands, they don't know what their team mates are going to play, they have to constantly readjust their thinking to utilize the knowledge they have to build the knowledge of the team as a whole. Cooperative learning gives students a new tool they can add to their learning kit that can help them in school, in their homes, and in their own personal futures.