FXG get compiled into raw code. So it gets accessed a lot faster in the application.
I think the compiler has some optimizations for it as well (file size).
So is your FXG text document 2400 bytes, or is the compiled version of the FXG file 2400 bytes (after being converted to Flash primitive opcodes and embedded in your SWF)...
Another reason to stick with FXG is that it's a vector asset which can be scaled without losing quality.
I was just looking at the FXG file by itself.
When compiled into the app it didn't add too much more to the app. So it doesn't seem to bad.
Are there any limitations or pitfalls in using FXG? Can you use them for rollover or skins?