It allows for go, no-go decisions at each stage to take advantage of new knowledge or changing societal priorities.
ɪɾ ɐlˈaʊz fɔːɹ ɡˈoʊ, nˈoʊɡˌoʊ dᵻsˈɪʒənz æɾ ˈiːtʃ stˈeɪdʒ tə tˈeɪk ɐdvˈæntɪdʒ ʌv nˈuː nˈɑːlɪdʒ ɔːɹ tʃˈeɪndʒɪŋ səsˈaɪəɾəl pɹaɪˈɔːɹᵻɾiz.