I've been composing for a local flute ensemble. They have a quite particular instrumentation -- two piccolos, about ten C flutes, two alto flutes, a bass flute, and a cello. In my composition I have to take the number of each instruments into balancing consideration. Say, for a rich bassy chord, there might not be enough low-pitched notes to support ten C flutes in the upper register. One solution is to divide the C flutes into more parts, yielding to a, say, 7-part chordal structure. The other obvious solution is to ask only part of C flutists to play, instead of all.

Dividing the C flutes into more parts has a problem: the score then will be too specific to adapt on other settings (I guess this nature provides the job market for arrangers). The other extreme is jazz charts -- the most flexible form of composition. I envy Hiromi Uehara that she can only write guidelines in her composition yet her guidelines are more specific than a jazz chart that the produced work still has a controlled overall structure.

Asking only part of the players to play makes me wonder that if a composer doesn't note how many players s/he wants for a part (quite common in an ensemble score), the balancing is really up to the conductors/performers. I believe an educated conductor/performer will make proper decisions on that. On the other hand, this also reminds me one of the significance of musical iconology. These scholars dig valuable information out of pictures. By looking at an early picture with a band in the background, they can decide the partial balance of an ensemble work. Amazing, isn't it?