Why do some doctors liposuction behind the ear and chin versus other doctors who focus on the chin alone?

Hello thanks for your question. The Entry points used for liposuction depends on the amount of fat and location of fat in neck. For minimal fat deposits a single entry point at chin would be sufficient. For greater  fat deposits to achieve crisscrossing and better skin retraction entry point at ear may be made. Hope this helps. 

 Most patients have fatty deposits throughout the neck and jaw line located below the ears, angle of the mandible and  the central part of the chin. It's also important to remember that  fatty deposits  are located at both above and below the platysma muscle.  Surgery is required for fat removal below the muscle along with a platysma plasty.  If significant lateral fat in the neck is left behind,  a bullfrog appearance will be the end result. For many examples, please see the link and the video below

 Hi, I have performed many facial shaping procedures using dermal fillers, facial implants (cheek, chin), liposuction and/or facelifts for over 30 years.  There are various places to make liposuction entry points for cannula placement for liposuction of the neck.  This depends on the amount of fat, whether its just located below the chin or all across the neck and the surgeon performing the liposuction.   I have performed many Chin Augmentations using chin implants for over 30 years.  If your chin is weak, this creates an imbalance making the nose appear larger, the mid face top heavy and the lower face look short that de-emphasizes the lips and allows early formation of a double chin.  Chin augmentation using a chin implant will add projection to the chin creating harmony and balance to the lower face. 
 I have found that placement of a silastic chin implant, through a small curved incision under the chin (also allows excess skin removal) to be very safe, quick, highly effective and far less invasive than a sliding genioplasty.  I perform chin implant surgery in 30 minutes or less, often using a local anesthetic alone.  Hope this helps.