When it's in the contract, then it means that when you break the law you both break the law and the contract. SHould it be necessary? Perhaps not, but in some places that makes a meaningful difference.
But if you are paranoid you should speak with a lawyer in your jurisdiction.
"Do not iron clothes while on body" should not be required to not be found liable, but it does change the question in court from providing discovery for safety consideration, how comprehensive is the manual, how... and the costs involved with that to "Did the customer use the device in a way that was it was clearly labelled to not be used? Did any part of the product packaging or instructions contradict this warning? ...Dismissed".
Like, yeah it's illegal to do illegal stuff with or without the label, but at least Lysol could say "we did tell him that he can't use it for that."