Why does an empty loop use so much processor time?

Question

If I have an empty while loop in my code such as:

while(true);

It will drive the processor usage up to about 25%. However if I do the followin

Answer 1

Because you're keeping the processor busy evaluating the loop over annd over.

Using Sleep actually lets other threads execute on the CPU and along with a very short context switch looks as if the CPU is free for a short while.