Dipping coral is a way to help prevent damaging pests from entering your tank system. An example would be zoanthid eating nudibranches. These guys will, as their name implies, eat zoanthids. Getting them into a system full of zoanthids is just asking for a TON of trouble as they can be easy to miss and multiply quickly. By dipping them (on top of quarantining them) helps prevent this to a degree.
I'm not sure with the rest of your question. I've dipped leathers, zoanthids/palys, and Acropora before in freshwater with Lugols added (40 drops per gallon) for 15 minutes. They did well. Never tried LPS. Maybe someone else can come along and shed some more light on the situation better than I.