event handlers: synchronous vs. asynchronous

[HC5]

In SharePoint, what's the difference between a synchronous and an asynchronous event handler? Is one more convenient to use than the other?

[suwunk]

Synchronous: happens 'before' the actual event, you have the HttpContext and you can show an error message in the browser and cancel the event

Asynchronous: happens 'after' the actual event, there's no HttpContext and you cannot directly show an error message or cancel the event

Check out this following blog post for the details:
Steven Van de Craen's Blog - Synchronous and asynchronous Event Handlers