Because if you immediately announce that you are done coding, you cannot do any of the other things on the list, which are all good ideas. After you've done the

Because if you immediately announce that you are done coding, you cannot do any of the other things on the list, which are all good ideas. After you've done them all, you should announce you are ready. It's probably a good idea to tell the interviewer what you are doing, don't just stand there looking at your code in silence if you can avoid it.