In order to reflect being "unique / Like a snowflake, distinct among snowflakes" at the beginning of "Helplessness Blues," there's only one voice and one guitar. After the lines "I'd rather be / A functioning cog in some great machinery / Serving something beyond me," a second voice, a second guitar, and harmonium are introduced in order to illustrate the opposite view. Later, this second guitar drops out before the line "If I know only one thing," so again there's a sense of singularity.
The strumming in the guitar parts also corresponds to the number. For the most part, if there's only one guitar, the strums are downward, and if there are two, the strums are upward and downward.