Question: Could anyone please explain what is the best practice of using itemrendrers for Adv. DataGrid in Flex? Should one use tag and write the component or by using itemrenderer property?

Regards,
Wrinkle

Answer: 
IMHO you should factor out the itemrenderer.
Look at it as an investment in the long-term maintainability and modularity of your code.
It could be that if you wrote the renderer generic enough, you could reuse it elsewhere in that project, or in future projects.

(I am assuming a non-trivial item-renderer - e.g. one that inherits from Label and changes the color)
No difference in performance.

Small difference in readability: if your renderer is rather small, there's no point extracting it as separate class. And vice-versa, if renderer grows huge, leaving its internals inside `DataGrid` tag may look awfull.