Our main goal with Plotly Express was to make it easier to use Plotly.py for exploration and rapid iteration.
Plotly was already, IMO, the most flexible / powerful charting library out there. If you had used its Python API, though, you know that it was rather arduous. It helped you build the perfect visualization, but it was too verbose to iterate quickly between a host of options. As a practitioner, you likely find yourself doing quite a lot of the latter.
Take a look at the examples in the post. Same powerful charting framework, but now it plugs directly into a tidy dataframe and allows configuration in a mechanism that you’ll be familiar with if you’ve used ggplot2 or Seaborn. Huge, useful improvement.