This is a much debated question. According to information from the Indiana State Department of Health and the Environmental Protection Agency:
There are well over 1000 different septic tank additives on the market, but there is no standard for testing them.
There is no evidence proving that a septic tank that is designed, operated, and maintained properly needs an additive to work effectively.
There is no product available that will allow a homeowner to escape regular pumping of the septic tank.
Some additives may actually harm your septic tank and/or absorption field.
There are products that can cause groundwater contamination.