Why do we need the directly call in a thread-safe call block?

Refer the thread-safe call tutorial at MSDN, have a look at following statments:

// InvokeRequired required compares the thread ID of the
 // calling thread to the thread ID of the creating thread.
 // If these threads are different, it returns true.
 if (this.textBox1.InvokeRequired) { 
     SetTextCallback d = new SetTextCallback(SetText);
     this.Invoke(d, new object[] { text });
 } else {
     this.textBox1.Text = text;
 }
 

Of course, I've used it many times in my codes, and understand a little why to use it.
But I still have some unclear questions about those statements, so anybody help me to find them out, please.

The questions are:

1. Will the code can run correctly with the statements in the if body only? I tried and seems it just cause the problem if the control is not initialize completely. I don't know is there more problem?


2. Which the advantage of calling method directly (else body) instance via invoker? Does it save resource (CPU, RAM) or something?

Thanks!

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