Is there any harm in plagarizing your "OWN" work?

Technically speaking, copying your own words does not constitute plagiarism, because to plagiarize means to copy the works of someone else and claim them as your own. However, doing what you are suggesting is high frowned upon. It falls under the definition of Academic Dishonesty, because each time you are asked to write a paper or give a speech, it is expected that you will provide new, original work. If all you do is copy what you've already done before, you are not giving yourself the opportunity to learn something new; nor have you really completed the assignment, which could result in an F. Dude, just write something new, even if it sounds highly similar to what you've written before. It is always better to be safe than sorry!

Yes, some people have gotten in quite a lot of trouble recycling their old work. At some schools, students can get expelled for it the first time they get caught.

Go read the academic integrity policy for your school. The information you're looking for may be in there. But even if this isn't treated as a form of academic dishonesty, I wouldn't do it. It's a great way of announcing to your professor, "I'm doing my very best to minimize the amount of work I am doing for this class," this professor undoubtedly knows most or all of your other professors, and a grad student really doesn't need a reputation for not working hard. Even if the questions are exactly the same, that does not mean the answers have to be exactly the same, and you would not have been accepted as a grad student if the faculty in your program didn't think you were capable of coming up with a new way to approach old questions.

If it is your own work you are copying, technically it is not plagiarism. However, on the chance your professor has a good enough memory to recognize regurgitated material, you might consider enough of a rewrite to at least look different

Plagerize your own work if it received a good grade before but it wouldn't hurt to re-write it a bit. Don't just cut and paste and you suggest.