[jacksonkmarley]

As it says in the notes that you linked to:

> In distributed systems, it is frequently unnecessary to know when something happened in a global context. Instead, it is only necessary to know the order of events. And often times it is only necessary to know the order of certain events, such as those that are visible to a particular host.

They are talking about logical clock implementations as a way to avoid having to build a potentially expensive sychronised 'physical clock' system with sufficient accuracy and security for the application.

The notes also talk about ways to get higher accuracy synchronisation.