Is Redundancy Necessary to Reduce Delay?

Logic optimization procedures principally attempt to optimize three criteria: performance, area and testability. The relationship between area optimization and testability has recently been explored. As to the relationship between performance and testability, experience has shown that performance optimizations can, and do in practice, introduce single stuck-at-fault redundancies into designs. Are these redundancies necessary to increase performance or are they only an unnecessary byproduct of performance optimization?