Many of the tales within are retold in The Silmarillion, albeit in modified forms; the work also contains a summary of the events of The Lord of the Rings told from a less personal perspective.

As with The Silmarillion, Tolkien's son Christopher edited and published Unfinished Tales before he had finished his study of the materials in his father's archive.

Versions of such tales, including the origins of Gandalf and the other Istari (Wizards), the death of Isildur and the loss of the One Ring in the Gladden Fields, and the founding of the kingdom of Rohan, help expand knowledge about Middle-earth.

The scholar Paul H. Kocher, reviewing Unfinished Tales in Mythlore, noted that all the stories are linked to either The Silmarillion, Akallabeth or The Lord of the Rings, and extensively annotated, mainly by Christopher Tolkien.

Olson comments that the book's commercial success demonstrated the existence of a market for more of Tolkien's writings, opening up a route to publication of The History of Middle-earth.

Where Bilbo is interested in food and comfort, and sometimes other familiar things such as riddles, she writes, Gandalf is concerned with defending the West against the Shadow (Sauron).

Elements of Gandalf's motivations and previous discussions with Thorin also find their way into the 2012 film An Unexpected Journey as dialogue, particularly in the meeting held in Bilbo's house.

In their view, the Quest "closely and thoroughly connects the action of The Hobbit with the larger, cosmic concerns of its sequel, showing how the Dwarves' struggle to regain their homeland became crucial in frustrating Sauron's plan to attack Lorien and Rivendell."