From the foreword to The Lord of the Rings. Here are some parts containing interesting ideas.
"I should like to say something here with reference to the many opinions or guesses that I have received or have read concerning the motives and meaning of the tale. The prime motive was the desire of a tale-teller to try his hand at a really long story that would hold the attention of readers, amuse them, delight them, and at times maybe excite them or deeply move them. As a guide I had only my own feelings for what is appealing or moving, (...)"
Deeply move! That's an essential point about the epic.
"As for any inner meaning or 'message', it has in the intention of the author none. It is neither allegorical nor topical. As the story grew it put down roots (into the past) and threw out unexpected branches (...)" -- Then the author justifies there was no allegory of the war implied.
Allegory and Applicability
"Other arrangements could be devised according to the tastes or views of those who like allegory or topical reference. But I cordially dislike allegory in all its manifestations, and always have done so since I grew old and wary enough to detect its presence. I much prefer history, true or feigned, with its varied applicability to the thought and experience of readers. I think that many confuse 'applicability' with 'allegory'; but the one resides in the freedom of the reader, and the other in the purposed domination of the author.
An author cannot of course remain wholly unaffected by his experience, but the ways in which a story-germ uses the soil of experience are extremely complex, and attempts to define the process are at best guesses from evidence that is inadequate and ambiguous."
In this passage the writer attempts to draw the line between 'allegory' and 'applicability' as a means of expression, also clarifying why he dislikes 'allegory'.
"The purposed domination of the author", that's what Tolkien dislikes about allegory. As I gather, the man disliked any imposing, concerning his Christian faith, too he did speak about Christian values in his works, but, say, through through the characters' actions and situation, not through declaring the ideas.
As it seems, if the question of allegory and applicability is looked on and developed from the above mentioned positions, 'allegory' in this sense is often mixed up with 'applicability', because if there's an image in the story (a symbolic image), it can mean several things, from which is for the reader (and the author) to choose (or not to choose).
If anyone has something to say about the topic, feel free.