Anyone find sequence diagrams useful? I’m working with a BA who loves creating these things—he has a tool he knows and clearly wants to get his money’s worth.

Just seems like busy work to me. Takes more time to understand them than if he just explained the concept in text.

In electronics it helps to describe the algorithm when there is a provided timing diagram next to it. Since some algorthms do rely on physical properties of the device.

I fiind them useful for showing the interaction between multiple services. Especially for people who aren't in the topic.

I like it for simple interfaces with complex flows, like git.

It is useful to in my case

it helps to explain protocol flows. e.g. OAuth 2.0 RFC uses a simplified ASCII collab diagram.

Yup, for non-trivial operations, it beats the text-only version (IMO).

If the diagram is harder to understand than the text, then the problem isn’t the concept of sequence diagrams, it’s the person generating the diagrams.

For a lot of situations it is. I've only found it useful in two situations of my career.
One is git flows the other was complex interaction with multiple systems for a single task.
Depends on what you do and have to communicate but yeah I would say it's one of the diagrams that in most fields isn't very useful often.