In my experience, unfixed charcoal drawings are extremely vulnerable to surface damage - the slightest movement can dislodge particles, reducing the intensity of tone, and dirtying highlights. An accidental touch can leave a noticable smudge. Even if a drawing is framed, movement, vibration and temperature change can still affect the drawing, and the drawing must still be transported to and handled by the framer.
The hardiness of a charcoal drawing can be slightly improved by choosing a toothy, velvety paper that grips the particles well. Willow and vine charcoals tend to be very delicate, while compressed and pencil charcoals are a little stickier.
For best results, carefully apply a couple of very light coats of fixative, and if need be, retouch the drawing afterwards (the fixative can act as a 'glue' underneath the charcoal).
The major error that people make when using fixative is to apply a heavy coat that saturates the paper and makes the particles of charcoal float into the grain of the paper.
Find out how to apply spray fixative