Does your charity co-operate closely with other charities? And if you do, how does it work for you?

Hello, I am curious to know about other peoples experiences. As a general rule of thumb, I suspect that working co-operatively with other charities is likely to be more productive and more cost effective than working alone. In practice, I sense there is a lot of reluctance, defensiveness around getting too close to other charities - Might they learn too much about us? Might we be more likely to compete with them. I sense that the more similar the other charity is the more discomfort there is. Interested to hear about other peoples' experiences. Thanks.