What are the drawbacks of using synchronous ajax call?

Question

This question could surely be applied to jQuery but in this case I am referring to Prototype. In the Prototype doc it says,

Since synchronous usage is

Answer 1

Most people frown upon synchronous ajax calls because it'll freeze the UI up until it has completed, as it will not allow code to continue until it's completion. Makes for a stutter in the interface I guess you could say.