The article also looks at the economics and business practices behind the adulteration of heroin. Obviously, taking advantage of the lack of quality control and getting more money out of less actual expensive heroin is a major consideration for the dealers, but it isn't the only one:
Interestingly, the paper also notes that professional heroin cutters are expensive, charging up to $20,000 for a kilo of heroin. This is likely due to the skill and knowledge needed to select ingredients that will have certain effects, which can be different for 'smokers', 'snorters' and 'injectors'.
Additionally, some ingredients are added purely for their psychoactive effect to give a different experience and 'brand' the dope.