What kind of harm can koan answers cause to one's practice? In a recent meta discussion some people expressed the opinion that giving koan answers may be detrimental to one's practice. In what way, exactly? And if it is so, why did many Buddhists publish koan commentaries for many hundred years?
I like to compare Koans with poems, or with jokes. Poems teach us to experience the world directly, unmediated by discursive analytical thinking, as feelings and associations. Getting a joke requires expanding one's context, relating alternative frames of reference.

In some professional settings, the experts develop a shortcut way of referring to things they deal with. E.g. in software engineering, you could hear someone saying that a particular design is kludgy, or leaking, or tangled up etc. Not all of these have official agreed-upon definitions, and many are made up ad-hoc, as required for communicating in a particular situation.

The method of Zen is to get practitioner in touch with their immediate experiences (to point them to their own mind). This requires transcending whatever context the person is stuck in, and expanding one's awareness to include "the elephant in the room". To build on the joke metaphor, the point of Koans is to make you "laugh".

Now, you can answer your own question: will explaining jokes help you learn how to laugh? Will analyzing songs help you learn how to feel?

Why did many Buddhists publish koan commentaries for many hundred years? -- I don't know. Because they are slaves of their minds? Because they think it may be helpful to certain types of practitioners?

The other problem with explaining Koans is that a Koan (unlike a joke) does not have a single "correct" interpretation. A Koan is always ambiguous, by design. A good koan commentary may help one explore various facets of the theme. Sort of like analyzing poems in school may(!) help one develop artistic sensitivity. But in context of Buddhism S.E. the danger is, someone might read an answer and assume they now know what this Koan is about.

Many people don't see until they know what to look for. I may not see a frog under my feet until my wife points it out, even though I've been staring directly at it. What we want to learn in Zen is to "see" before knowing. The more you explain Zen, the further you are from "seeing".