For some forums that are not open to the public it's useful. Otherwise it's best to disable.
You seem to agree with me now that making the HTML permission safe would be hard if not impossible.
Not sure if this last statement is correct, I do not know enough about it to comment on that. I just know that javascript will be disabled if HTML is disabled, that what this was about.
Thanks for your comments, I'd like to hear from others now if you don't mind