This is all about visibility! The Royal Wulff doesn’t really imitate anything; it’s just an attractor pattern. In fact, if you are fishing on a day that the trout are being very selective or in the middle of a hatch, this pattern will probably frustrate you as many fish will seem to go out of their way to avoid it. I find this pattern works best in rougher water and on days when the trout are actively feeding. It’s really easy to spot, which is a very good thing in the foam! You want to keep it moving quickly so avoid attempting this one in slow moving pools.
As far as tying this pattern, it takes a lot of patience for someone new to the hobby. There are several technical aspects to the fly all happening in a very small space.