We actually did not add this option to our site selectively, and I cannot really explain any more about what it does than queenofcollectibles described (and I confirmed) above. Our description editor is developed by a third party, and this new option appears to have been included as part of the latest update that was made available to us.
I certainly understand your inquisitiveness but, based on the conditions under which I have seen this option appear, I am uncertain why it would cause you any difficulties. However, I also have not seen the specific circumstances under which you have seen this option appear.
If this option is causing you to have trouble creating or editing your descriptions, please contact our Customer Support team directly and let us know as much detail as possible about the issue you are struggling with and we will do our best to help you out.