Complements are pervasive in industries. A firm must know what complementary products it depends on, and how they affect its competitive advantage and the structure of the industry as a whole. A firm must decide which complements it should produce itself, and how to package and price them. Bundling and unbundling of complements is one of the ways in which fundamental industry restructuring takes place. The challenge is to make strategy towards complements an opportunity rather than a source of competitive advantage for competitors.
Source: Porter Michael E. (1998), Competitive Advantage: Creating and Sustaining Superior Performance, Free Press; Illustrated edition.