What I have learned about data viz over the years is that it is a very powerful solution to problems, just as Nightingale's diagrams demonstrated the effect of hygiene, which changed how societies and governments respond to epidemics. What I have also learned is that a solution obviates a dynamic someone thinks it is their job to manage, and a visualization that solves a problem is its own problem.

The "best," diagrams show change over time, and provide the presenter with a way to demonstrate how they are the important pivot point that optimizes and drives that change. The "worst," diagrams are the ones that illuminate the problem in such a way that it is no longer difficult, which humiliates the people it was presented to and designed to help.

I recommend using data viz privately, to reason through and solve problems quickly, and then use the time you save for self investment. The real value I think is to use data viz not as a product for productivity, but as an arbitrage tool for leverage.