In the case of omniscient POV, a number of persons in a chapter can think, feel and see. In 3rd person point of view only one person in a chapter can do all those things. So you can describe only what one person sees and write only about that person’s feelings and thoughts. Some practice is necessary for this, but gradually the rule gets under your skin. And it produces a stronger emotional reaction in the reader. All the books on creative writing recommend 3rd person POV.