MOTM

>I have the choice know of setting the second voice to double the first
>if only one note is pressed or to remain silent.

Both configurations are useful. If I could only choose one, I'd 
choose the former (double the first if only one note is pressed) 
because it will retain a more constant volume with both voices 
playing in unison, and single note runs will be fatter with both 
voices playing in unison.