For the majority of the flies I tie, I rarely use head cement on my whip finish. But if I am tying a saltwater fly or a larger streamer type pattern, I do like to put a drop of my favorite glue, Liquid Fusion, on to help increase the durability. Most people put the head cement on after they have finished the fly with a whip finish. I like to add it before I tie the knot. I will put a drop on the head before my last few thread wraps. I then do thread wraps over the dollop of glue, spreading it throughout the entire head of the fly, before I whip finish. This gets the glue inside the knot instead of just on the surface. I believe it helps even further increase the durability of the fly. Happy tying!