"if tensioned properly" (with my tarps), the continuous rl could be slack under the tarp anyway, as you want all the tension on the structural RL seam of the WB tarp, however if most tension is on the seperate RL instead, the RL seam of the tarp may not be tight enough, and the tarp may not fully perform. same thing goes for folks using shockcord or any elastic tarp tensioner on the ground corners. the tarp will perform best when there's a good 30-40 LBS of force on each ground corner guylines,(i'm just guessing on the force, but it does great when pitched pretty darn tight) this stretches the fabric so it doesn't sag in the middle of the night, and keeps it taut so it performs better in wind. i'd bet 95% of those using elastic tensioners aren't pitching their tarp tight enough for max performance.
i've heard alot of folks say centering their tarp without a continuous RL to slide it on is difficult. i disagree with that too. most of the time you setup it isn't raining, so you'd probably set your hammock up first. say for instance you know your hammock RL is 100" and your tarp RL is 132", that's a difference of 32", (or 16" overlap at each end). just set up the first end of the tarp so it's got 16" of overlap past the end of the hammock (about mid-finger to elbow for me) and the other end will automatically be about the same. if you setup in the rain and set your tarp up first, it's just as easy if not easier. simply adjust your hammock instead of the tarp. I know all you continuous RL folks are using buckles or whoopies on your hammocks anyway so adjustment there is easy