At the bottom of this post there's a before-and-after exercise*. The original, on the left, comes from Spain's eldiario.es. Just for the record, I have mindlessly done tons of parliament charts like that in the past. The “mindlessly” part of that sentence is critical, as I was mimicking what many news infographics designers were doing.
But one day I actually tried to read the parliament-looking chart, and make comparisons. I couldn't. I needed to read every single figure to be able to mentally visualize variations.
You can see the evidence yourself. Read just one or two figures in the first chart below, force yourself not to read the rest, and then try to estimate changes accurately. Good luck with that.
So the parliament chart is nearly useless; a table would've been better. This chart is more a nice-looking abstract illustration than a visualization because a visualization should be an aid to understanding, not a hurdle.
*NOTE: I made a slope chart, but I'd be fine with a bar chart, a dot plot —or even a divided bar chart (suggestion inspired by Clement Levallois)