1. Image Resizing
  2. Resizing images forces CPU and memory
  3. Mobile devices download non-viewable data
  4. Mobile speed vs. Desktop speed
  5. Hiding background images is a bad idea
  6. More code, more to update
  7. CSS media queries will not remove unnecessary code (JavaScript or html)
  8. CSS media query is a bad choice for multiple devices
  9. "Great mobile products are created, never ported"
  10. Mobile needs are different from desktop needs
  11. Better create a mobile website than a responsive one

See : http://goo.gl/K35RX