First, unless you are using RemoteObject, you data is
probably XML already. resultFormat="object", the default, causes
Flex to attempt to convert your xml into an nested object
structure. This is a "black box" behavior. Predicting the output
structure is difficult. This conversion also takes time.
Second, e4x XML has huge functionality built in. You can
search, filter the data efficiently and easily. You will have to
write recursive functions to do that with a nested object
XML is easily handled in XMLList and XMLListCollection
objects with their methods. With object you have to do it all
Finally, AS is very fast. Performance is always a good thing,
but until you are an expert on issues like when to use
cacheAsBitmap, you will be better served focusing on UI rendereing
performance, not machine cycles.