Sigma factors play an important role in spore formation, ensuring each step in the process is complete prior to the next step starting. This ensures successful spore formation, with opportunities for error correction at every stage.
Having checks in place with spore formation is important – it must be done correctly for the survival of the bacterial population. If spore formation were to go wrong, it could prevent successful sporulation and lead to the extinction of the species.
Different proteins are required at different points in the sporulation cycle, and a sigma cascade is the most efficient way of controlling this in bacteria. Sigma cascades are used in many bacterial processes, including the formation of flagella (using FliA as the regulatory protein).