"What benefit for the mind does this mix allow?"
Thats a pretty personal question and varies between each individual and each experience. it has the potential for many benefits IMO. You won't notice much of a difference unless its something like 10x caapi changa though. I find it much more mushroom or ayahuasca like than just crytalline freebase on its own. It feels more smooth and integrative to me, and there is much more intellectual/spiritual/emotional insight even on just low doses when compared to just dmt. But yeah many have differing opinions on how the "mind benefits from changa" and most of it is left up to set/setting. IME imagination/memory/visualizing/mood/perspective/mind-body integration/etc can all be effected. One thing you can count on though is that is will affect you're mental processes to a greater degree and the length will be longer.
"What kind of setting would be suggested to get the very most benefit out of it?"
Whatever you feel is the best for you. The same setting you've had for freebase is probably a good start- not sure why there needs to be a difference really. I love changa in a secure and safe location outdoors the best, with the sunlight coming through my eyelids.
Really though, i wouldn't worry about the difference or over think it. Just experience it and see for yourself how you like it
<Ringworm>hehehe, it's all fun and games till someone loses an "I"