Synchronous vs Asynchronous Clients (Explained by Example)

In this video we discuss the difference between synchronous and asynchronous user experiences. What are the advantages and disadvantages of both. We have picked YouTube uploading page as an example for this video as it perfectly describes the asynchronous nature of user experiences. We explain how that page would have been written if it was synchronous.
Question of the day: Do you code prefer the synchronous or asynchronous pattern and why? Thanks!