First, a slightly late response to Phil Edwards, who challenged my saying
"Someone who wants to use chords, but hasn't the ability to choose chords that are at least adequate to fit a given melody, probably also wouldn't know how to transpose to the corresponding chords for a different key if the original key is unsuited to their voice."

I did say "adequate" and "probably". I find it hard to believe that there can be many people who know how to transpose but can't manage even the "three chord trick". (Or the two chord trick on a one-row melodeon!)

As for wanting to know exactly what chords a particular performer has used: I take the point that there can be valid reasons for that. But sometimes the request seems to mean just "please tell me what chords to use for X", which seems simplistic.

Richard