Why is GUID attribute needed in the first place?

Question

What is the necessity for the GUID attribute? why don\'t just let the compiler handle this automatically?!

Answer 1

You can do it (just omit the attribute) but then the compiler will generate a new GUID on each recompile even if the interface has not changed. That's unfortunate because the users of that interface don't know about the change and will retrieve the interface by it's old GUID and will therefore fail to retrieve it.