I still don't have enough experiences with smoking and ayahuasca to give my definitive opinion, but during ayahuasca trips I feel a great need for the loving presence of my partner. When I've smoked it, I was actually on a long journey to reunite myself with her and on the way I stopped at a park and smoked some changa. I saw visions of my partner but otherwise didn't feel the longing for companionship that I felt while on ayahuasca. I feel very empathetic while on ayahuasca, I feel the loneliness of my existence, and a sense that community is the only real way to comfort ourselves in front of the terrors of the void. The sounds of the neighbors talking and eating is one of my favorite parts of my recent ayahuasca trips, but I only really feel their presence as an abstract community far away. I suppose that's why I like to have someone with me while on ayahuasca. Perhaps this differs from DMT because ayahuasca is much more of a challenge.
On the other hand I've also smoked in the presence of others that were uninitiated and staring at me, and it made me feel very awkward. But then again when I've smoked with my brother who was also partaking, and that was great.
So I'd say that having a sitter is on the whole good, as long as they are people you feel comfortable with on a deep level.