The "Link to my Yahoo! ID" box lets you choose whether or not you want to allow access to your Yahoo! Profile or not.

Information in your Yahoo! Profile is publicly available, and may include information about yourself that you've posted including your name, address, email address and associated instant messenger (IM) account.

If you have an email address and/or an active IM account associated with your Yahoo! Profile and don't want anyone to email or IM you about the review you've written, leave the "Link to my Yahoo! ID" box unchecked. If you've set up an email address or IM account with your Yahoo! Profile and choose to allow readers to email or IM you regarding your comments, check the "Link to my Yahoo! ID" box.