Why do some planes not have winglets?

Related questions

1. How do sharklet materials grow bacteria?
2. What is the difference between a sharklet and a winglet?
3. What does Sharklets mean?
4. Do winglets reduce turbulence?
5. What is a320 sharklet?
6. What are sharklets on a plane?
7. Why are airplane wings tipped up at the end?
8. Does Airbus a321 have power outlets?
9. How long does it take to refuel an a320?
10. How does the 747 lift off the ground?

Tags

1. #reduce
2. #smaller
3. #which
4. #vortices
5. #wings
6. #following
7. #large
8. #translates
9. #plane
10. #winglets
11. #turbulence
12. #closely
13. #breaking
14. #created
15. #called
16. #their
17. #savings
18. #strong
19. #enough
20. #airplane
21. #purpose