The AFL is as much as comparing apples to apples as it is for developmental purposes. You get to see six of the top prospects from each organization play with and against like-minded players.
Yes, they may be working on specific things but it's more of a trial-run for major league scouts to see how close these players are to the big-leagues as well as a place for other teams to scout prospects for future trades.
For those that love baseball, the AFL is a hidden jewel that is a must-see. It's kind of where spring training was 20 years ago before it became so popular. The talent is amazing and the crowd is usually about 150 people, half of them scouts! I have made it a point to watch the last six years in a row or so and highly recommend it for serious baseball fans.