Many tunes (both fiddle type tunes and songs) imply chords. But many do NOT do so at all. In many such cases, putting chords under the tune butchers it -- my opinion of course. English dance tunes often are very chordal in nature, Irish tunes often not, thus accompaniments are often not too much more than one chord, and players of things like bouzouki are often playing the tune with some drone strings sounding. To force standard chords on to these, in my opinion, does real harm, and one needs to provide supporting accompaniment (if at all) with considerably more skill and taste then "Where do I change from C to G?".

This is perhaps even more true for the songs. Listen (among countless others) to some of the old ballads on the Jean Ritchie ballad records from folkways (now reissued   on CD and available from Jean and George). TO put chords under these would be a complete nightmare. . .

One of the signs of good taste is knowning when to leave things alone. Unaccompanied songs or tunes are not necessarily missing something.