From our Four Strong Winds lesson comes a good opportunity to visit a topic from the fingerpicking world, which is whether to pick the note as the open string versus put a finger down on a fret to sound the note.
It all depends on the effect you want or need. In 4SW, there are a lot of sustained notes. Guitar doesn't handle sustain well, nylon strings hand sustain worse than steel strings. (Maybe a chorus effect on an amp or some kind of pedal. But not everyone has that setup. And I don't know anything about electric guitars.)
Violin as a stringed instrument can kind of faux infinite sustain by drawing the bow in long strokes back and forth over the string. Mandolin can faux long sustain a long time too with tremolo. There's of course tremolo on guitar, but it's not top of the new learner's tool kit.
A simple technique we unplugged guitarists can use is vibrato. (Other string instruments, including ukulele, can use vibrato also.) This is that slight tremble where the note goes up and down in pitch by a micro tone. Singers do it by controlling air flow thru the diaphragm. String players do it by rotating a sort of flattened fingertip a very short distance back and forth over the note within the fret box.
There are variables that contribute to nicer vibrato. I recently replaced my string set, and vibrato came a lot easier on certain strings.
Some times you'll see players almost wiggle the whole instrument in the neck area against the fretted string, like they are trying to wring the last millisecond out of the note. And maybe they are!
There are a couple of spots in 4SW where you land on an open D and/or open G for a held note. (Verse at 'We've been thru that a hundred times or more,' and Chorus, "I'll look for you if I'm ever back this way.')
You could also opt to play these D and G notes by fretting them. An open string note can't be fretted, therefore vibrato'd. But a fretted string can.
Two other merits of a fretted vibrato note are: 1. it slows you down and reins you back from rushing. And 2. something is happening visually, creating the useful supporting 'illusion' that the song is still in motion, that a tone is being carefully considered and played, even if it doesn't ring a ton longer than the open string.
Open string notes are of course wonderful, they ring beautifully. But this may not be the best solution every time.
I've posted a few short video clips on YouTube to show the same phrase with open strings, then with vibrato on fretted strings. Start with Clip 1, 4SW phrase in Verse ending on Open String video, and the remaining 3 clips should autoplay:
To Fret or Not to Fret Clips, YouTube
Fretted strings can also *sometimes* have the advantage of not requiring a string crossing, thereby helping you to minimize chance of a mistake. But in this case, going from 4th string E to fretted D on the 5th string, you do have to cross strings. With a bit of practice, you will develop the muscle memory to start the reach for the 5th string D, also glancing at the neck, to ensure you hit the right string.
There's nothing wrong with playing the open D almost as a pull-off from the 2nd fret E note. But you are making a choice to just let the open D ring and die off when it wants to, rather than having more control over it. Ultimately the choice is yours.
Good talk!