Standard epithets ("bold William", "a lady gay") are handy for metre, as well as for rhyme schemes. Then there are what you could call verse-fillers, repetitions of entire lines in slightly different words to pad out a verse:

"You rise early tomorrow morning
Rise before the break of day
There you'll see your true love William
Walking with a lady gay."

Not to mention song-fillers - entire verses repeated with minor alterations, when the sense could have been conveyed by the words "and that's what he/she did":

"She rose early the morrow morning
She rose before the break of day
There she saw her true love William
Walking with a lady gay."

(Examples from William Taylor, of course.)

When you start to look at it, traditional songs are full of this kind of thing. It's quite alien to contemporary songwriters, which is why so much writing in a traditional style isn't. As you might say,

They try to write in a style so folk-ish
They try to write in a traditional style
With standard phrases and metre-padding
And repetition all the while

But they can't write in a style so folkish
They can't write in that traditional style
With standard phrases to pad the metre
And repetition all the while