I still diagram flowcharts. Usually to convey to one of my internal customers how we envision interfacing with a 3rd party system or solving some complex business logic.

I diagram a lot of things. Mostly for my benefit. I have struggled over the years with what symbol do I use for X but now I just pick a rectangle or predefined process rectangle and label it well. Diagramming helps me get my internal thoughts out and makes the systems I write better and less error prone.

This was also a point brought up in a recent talk [1] on software engineering, and what has happened since the "software crisis" was recognized in 1968.

The speaker, Mary Shaw, talks about Design Guidance, and how a decision chart is "a better organization of a body of design decision knowledge" [starts 27:40] and how we still, desperately, need something like that, and that there aren't any better ways to communicate such knowledge, that the speaker is aware of, than "this ancient chart."

(UML is mentioned later, but under the context that it is dying, which was probably a good thing.)

[1] Progress Toward an Engineering Discipline of Software https://www.youtube.com/watch?v=lLnsi522LS8

Diagramming also has the added benefit of being a more precise way of communication how a system works. I've found that a 30 minute discussion can be turned into a 2 minute explanation with the use of a diagram.

Personally, I can't even really think about complex business/application/system logic without drawing it out on a whiteboard.