It was developed to enhance nutrient absorption. Supplement companies typically add 5mg along with B6 to products to accomplish greater absorption increasing blood flow to the digestive tract.
Source Citation (MLA 7th Edition)
"Sabinsa granted third patent on Bioperine bioavailability enhancing phytonutrient." BIOTECH Patent News Dec. 1999. Health Reference Center Academic. Web. 26 Nov. 2012.
"Piperine Increases Serum Response of Beta-Carotene During 14 Days of Oral Beta Carotene Supplementation" (Nutrition Research Journal: March 1999).