Wholly apart from the mere harmonic translation of melody into orchestral sound, orchestrators also try to understand the composer’s intent. Questions such as these need to be answered:
Does the composer want to emphasize a light, optimistic view or foreshadow a coming tragedy?
What type of music has the composer written–a waltz, tango or polka?
What instruments are best suited to convey the harmonic sound and the composer’s intent? Are strings or woodwinds more appropriate? When do you use a bassoon or an oboe? A flute or a harp? Do you want to emphasize the dark vibrations of a cello or bass, accentuated by a kettledrum?