I suspect he uses two 'heads' because he is tying presentation grade Atlantic Salmon flies and with the two heads he most likely will not scratch nor mar the surface of the hook in any way. Those flies will sell for up to and even more than $350, depending upon what feathers and materials were used and how well known the tyer is. If you pay that much for a single fly that will be mounted for display, you don't want any scratches on the hook.

Larry ---sagefisher---