The purpose of the Sangha is to spread/protect the Dharma and allow others to gain Enlightenment. The relevance of the rules of conduct can thus be judged against these objectives.
Written rules did not exist until the early writings of the Pali Canon at the Fourth Buddhist council, nearly five centuries after the death of Siddhartha Gautama. Thus, written rules of conduct as we know them today clearly did were not needed. However, that is not to say that rules of conduct did not exist. Oral tradition maintained preserved the dharma and monastic rules to uphold their relevance long after Siddhartha’s death.
Strict rules of conduct vary amongst Buddhist schools depending on how literally the concept of a community of Buddhists is interpreted. Mahayana Buddhists interpret the Sangha as the collection of all Buddhists, transcending physical boundaries – with a lesser emphasis on a monastic community of Bhikkus and Bhikkunis, rules of conduct are less relevant. In contrast, the Theravadin Pali Canon views the Sangha as a physical communion, thus monastic rules are essential.
A.L. Dhammadharo argues the Vinaya rules of conduct provide the best environment for both personal understanding, the teaching of the Dharma to others and maintaining the integrity of doctrine. However, the Tendai school has a reduced set of rules with 60 rather than the 227 stated in the Vinaya, while Thich Nhat Hanh’s Order of Interbeing identifies just 14 rules – this would suggest there can be somewhat flexible approach to the rules of conduct, as long as central doctrinal principles are upheld. That said, reducing the number of rules does not necessarily reduce their relevance: more concise monastic rules may still carry the same significance.