On large flies with significant amounts of materials tied in at the head it matters. Think heavily dressed bucktails or similar flies made with synthetic wing materials. Binding in a rather large bunch of bucktail or squirrel tail makes a relatively large diameter head which is much more subject to torque and abrasion than a few tiny wraps holding down one hackle. We're not all living in a trout-centric universe. Head cement absolutely has many valid uses.