An omniscient narrator can freely report the thoughts, feelings and decisions of any character in the story without having to switch scenes or resort to any other device. This is not only convenient in communicating the basic flow of the characters' growth and experiences, but it also allows the author to set up strong dramatic ironies by letting the reader directly observe misunderstandings or conflicting viewpoints between characters who would not be able to report on the discrepancies from their own perspectives.
A story written from the perspective of a single character, whether in first or third person, is limited to narrating information that that character can observe. This can make it challenging to report important events for which the point of view character is not present or conscious, or which the character has no reason to notice. Omniscient narration has no such limitation. Instead, an omniscient narrator can report any relevant details of any occurrence in any setting regardless of which characters, if any, are present.
In earlier centuries, it was common for an author writing in omniscient narration to address the reader directly or comment on the action of the story from his own perspective. While this allowed the author to express his views very directly, it is a practice that has fallen into disfavor as heavy-handed. Nevertheless, when writing with omniscient narration you still have a greater opportunity than usual to slide in statements of fact or opinion that fit the situation but that none of the characters would have reason to think or express.
Deceptive narration is an advanced use of voice and point of view in which the author writes a story from a perspective that is knowingly skewed or calculated to create a false impression. In first-person narration you can use it to slowly reveal that the point of view character is a scoundrel, perhaps even the actual villain of the story. In omniscient narrative, however, there is potential for much deeper and subtler deceptive narration. Narrating carefully calculated contradictory accounts and factual discrepancies can create a sense of mystery or unreliability that, used properly, can be deeply dramatic and thought-provoking.