What is the purpose of an ab board after liposuction? Is it necessary to get one?

Each Doctor will have their own protocol following liposuction. My patients wear customized compression. For liposuction after care, I recommend adding hyperbaric oxygen and lymphatic massage along with your compression to help decrease swelling. To improve your final results, I also recommend adding vanquish for further fat removal, exilis/venus legacy for skin tightening, cellutone/z wave to make the skin smooth, remove scar tissue, and improve the skin’s appearance. See an expert. Best, Dr. Emer

As you may have gathered from other answers, not many physicians recommend or use the "ab board" you are referring to.     I have had a patient that purchased this type of garment, and they used it without any problem.   Generally, most physicians recommend using a compression garment and/or an abdominal binder after liposuction.     Follow your physicians instructions as to what they prefer.   I do not think a "board" is necessary personally.

I asked my patients to wear a compressive garments for about six weeks after liposuction. This is primarily for comfort. I doubt that garments of any kind affect the long-term outcome.

I perform several hundred liposuction procedures and BBLs each year, and I use a compression garment with three bands that can be serially tightened.   Ab boards may be effective, but I do not use them for my patients.   The plastic surgeon who is performing your lipo will have preferences; follow those as he or she will be monitoring your recovery.Kenneth Hughes, MD, Board Certified Plastic Surgeon Los Angeles, CA

it is helpful in keeping the skin around the belly button flat. Often the compression garments worn after liposuction have a tendency to create creases anteriorly. The board helps to flatten the skin of the abdomen allowing more uniform compression. 

I am not sure what an "ab board" is.  I am wondering if you were told "abdominal binder".  The binder helps stabilize your muscle repair, decreasing the tension on the sutures.  Make sure you discuss your concerns with you surgeon and simply ask the same question.  I have not heard the term and my suspicion is they were referring to the binder.  In our practice, we ask the patient to wear the binder for three weeks day and night, then three more weeks day only.  This way, we help decrease the tension on the muscle repair (major Tummy Tuck not mini).  I hope this helps.
Dr. Dillon

Abdominal boards help prevent creases.  This can benefit some patients, but not all.  Wearing a good compression garment is important for an optimal result.