To my understanding, it allows messages on the network to have a total order, even when fully decentralised. Without a hash chain, clients could not tell what o

To my understanding, it allows messages on the network to have a total order, even when fully decentralised. Without a hash chain, clients could not tell what order events happened in, and might display them ordered differently, which would change a conversation's meaning. The traditional alternative is logical clocks, but a malicious participant could forge those, so they're not suitable for a fully distributed system run by random users.