That's for parameters. There's also the front end of your URL, which may be either www.example.com or example.com. It makes a big mess if both versions are indexed.
Unless your Bing WMT is entirely different from mine, you can't just "enable" in the abstract. You have to specify parameters and then say which ones should be ignored. (Yes, OK, I tried it. Clicking on "enable" when you haven't named any parameters doesn't do anything.)
Hm, come to think of it, I do believe I just recently saw a question about that very subject elsewhere in this Forum ;)