The Debug Mode is for advanced troubleshooting your board,
you must use it only with your Board turned OFF.
If you leave it ON, a good hacker could grab all the data you don't want him to know about it... unless the board is OFF.
Even then, I don't like it to have it turned ON on a live setup. On my test board, is always ON.
You can start a new thread, asking what exacly does the Debug Mode in vBulletin.