I won't claim expertise, because I don't fish eggs under a bobber that often, but I do it often enough, and catch a few fish with it.

My experience is that eggs sink. If you are in smoothly flowing water, those eggs will be rolling pretty close to the bottom. I use a 2 ft leader to the eggs, and no weight below the swivel. This catches fish where I use it, which is smoothly flowing, cobble bottomed runs. I use a bobber in these runs because I'm trying to work a bait down into a spot that I can't otherwise get to.

Now, Bob gets paid for this, and I don't, so you might want to listen to what he says, but I hear he was really an English major in college, and makes all this stuff up anyway.