These disclaimers have never been tested in a courtroom, and in some circumstances they could even reduce your legal protection. However, I reckon the key issue for a business is “branding”.
Do you really want your communication with clients, suppliers and associates to look like your relationship will be defined by lawyers? That you routinely send “confidential” email to the wrong people and have to ask for it to be deleted? That you or your staff won’t actually stand behind what you say in an email because it’s not “confirmed in writing”? That your reaction when things go wrong is to sue someone?
Please, empower your staff to speak with authority. Get your act together so you don’t make lame mistakes to begin with. And have the confidence and honesty to stand behind what you say, wherever and however you say it.