Well I'm just going by what I read here:
http://www.thisismobility.com/blog/2...rmware-update/

"Disable RD mode using the flasher using ‘flasher-3.0-static –disable-rd-mode’. Power consumption and response times seem to really suffer with RD mode left on, so I always turn it back off now."

I've also read that R&D mode enables the serial port (beside the battery), which is a power drain. Looking at the Flasher parameters, I suspect R&D doesn't actually enable the serial port by default. But I can't think of a good reason to leave R&D mode on all the time. I just install "becomeroot" and that's all I need.