Ask HN: What software diagrams have made a difference I your decision making?

When it comes to diagrams in software development many things and opinions can be discussed, and often are, about the use of diagrams in software development (and -architecture): UML, not UML, C4, types of diagrams (e.g. class diagram vs component diagram etc), 4+1 model, level of detail, auto generate or not, and so on. All of the discussion is good, and there will never be one true answer.

What I would love to hear about is a very pragmatic and individual question:

What types of SW diagrams have actually made a difference for you/your team in a decision making situation?

I know that diagrams often have good use when it comes to explaining a system to a new hire, or other person not already familiar with the system.

I’m more curious if anyone have used diagrams in an analytical situation and as input to a design decision. Have you used diagrams in a way that gave you some insights into a problem that you couldn’t get just by taking about it? Have you used diagrams to show that solution A is better than solution B?