Flex: Should I use web service calls in custom components or regulate them to main.mxml?

Question

I'm attempting to code an RIA with loosely couple components. I have several custom components that use data from a web service I've decalred in main.mxml. As a best practice, should I make all of my web service calls in main and pass along the data to the components, or give the web service credentials to each component and let them make their own web service calls?

Thanks!