Originally Posted by Mustardman
That's one of the biggest selling points. It also helps protect from wind blown mist and splashback on your UQ. Not being totally waterproof it won't stop it if the wind is blowing sideways and drenching your hammock, but it helps you keep dry from the mist you get when using a smaller tarp.
I don't know that its really a selling point, though. Not like you would want to go with a Maccat Micro instead of your BMJ - or at least I wouldn't want to give up the square footage of coverage under the tarp - not as rain protection anyway.
Its not so much that you can carry a smaller tarp as much as you don't have to carry a gargantuan tarp like the Cloudburst or others that might fit over the RR in more the manner we're used to doing with a regular hammock. So really, you either need a larger tarp OR the Spindrift in addition to whatever you're now using in order to get equivalent coverage on the RR compared to what you might be used to (better coverage of course with the sock).
I got out with the RR and my Toxaway this past weekend, and the Tox fits fine over the RR, albeit with a very mild angle (around 45 degrees) to keep away from the spreaders. This angle leaves a pretty large opening at the ends where I would be concerned about getting wet. However, I think there is enough coverage on the Tox that an undercover might do.
Now, in colder weather where you don't really expect rain, then yes, you could go with a smaller tarp and the sock would replace the wind blocking of a larger tarp.