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)
There is one big difference, if you are debugging a component. In my case I am using IntelliJ and there seems to be an Issue (They claim it to be a Flash issue) that renders all Breakpoints invalid as soon as one inline component is found.