A rondo for example isn't just 4 players playing keep away from a single player and a bit of fun (though they Are fun), what you get out of a rondo is the following: 

1. Soccer Awareness: Assessing options BEFORE receiving the ball
2. Technique,
3. Mobility, 
4. Agility and balance
5. Body position, 
6. Foot preparation, 
7. Communication, 
8. The 1st touch, 
9. The 2nd touch, and beyond
10. Teamwork, 
11. Collective tactical understanding in a small sided game environment, 
12. Positioning OFF the ball, 
13. Problem solving, 
14. And developing creativity and imagination, 
15. Intensity of play, 
16. Physically challenging;
17. Developing Angles of support;
18. Opening up passing lanes by movement off the ball;
19. Speeding up thinking and decision making, The SKILL FACTOR;
20. Ultimately providing a competitive environment where no one wants to give the ball away and finally,  
21. They are fun to do.