There's a judo and sambo coach in Seattle, who practices BJJ, that does drills with his competitors where he makes them talk and respond to questions while sparring, as a way to work on cognitive ability while the body is in duress. He is also a firefighter, who does seminars on efficient response techniques during emergency situations, and a pillar of his philosophy is maintaining cognitive ability after your heart rate exceeds 160bpm, when your perception of the world narrows.
Talking, for me, is also a way to keep a playful atmosphere, especially when you don't know the other person. I've been able to diffuse a few go-tards while rolling by just saying a few things here and there.