Open Strings vs. Fretted Notes
On the guitar the same pitch can often be played on several strings in different positions on the neck. In standard tuning, the open string notes are E1, A1, D2, G2, B2, and E3 (the numbers indicate the octave; E3, for instance, is two octaves above E1). For those notes, you will often have a choice of playing either the fretted note or the open string note. Look at Example 1 and play each of the open strings and then the equivalent pitch as a fretted note found on the lower adjacent string (these are the same pairings you use to tune your strings). Logically enough, there is no fretted equivalent for the open sixth string.
The decision to use an open string or a fretted note might be based on a variety of considerations. One of those might simply be convenience. Is it easy to play? Another consideration is controlling note durations. Should each note end before the next begins, or should they be allowed to overlap? We’ve already seen how it’s possible to control notes with the picking hand and the fretting hand, so let’s look how these two considerations affect the choice of an open vs. a fretted note in a musical phrase.
Many of the notes in Example 2 are played open for convenience; it is less work for the fretting hand, and the notes fall comfortably under the picking hand. Play through the example allowing the open strings to ring, and you’ll hear it has a pleasing sound. However, if the nature of the music suggested that we maintain strict quarter-note durations, it would be necessary to stop the open strings with the picking-hand fingers. Play the exercise again very slowly, releasing fretted notes after their written values, and stopping the open strings with the finger that plucked them as you pluck the succeeding note. This makes the passage considerably more challenging.
Excerpted from The Alex de Grassi Fingerstyle Guitar Method