Section 8 is wood land it can get rather dark in some parts. It makes seeing where you are shooting easier and makes people put their head down a bit more.
I'd never even thought about using tracers outdoors, but I guess it does make sense. Section 8 don't appear to require bios, but I would stress that the Depot really do mean nothing over 0.25g, regardless of what's pewing them. I've not seen them weighing or monitoring BBs during the day (they supply 0.2g for chronoing), and I'd hope they're not going to be given any cause to start doing so.