I have long argued that this type of chart should be used sparingly. Notice that the key point of the chart requires comparing voice (or text) usage across age groups; this means readers are asked to compare the relative lengths of the blue (or green) bars. With grouped bars, readers are asked to literally jump over bars to perform the comparisons. The more groups, the more bars to jump. I don't like to exercise my readers in this way.
Something else more damaging is lurking beneath. We can see this by splitting up the charts. Here, I'm reproducing the two charts as is, but on a small multiples format.
Recall the key practical question here is to compare usage across age groups. Now look at the massive amounts of empty space on the Voice usage chart: the space crowds out the data, meaning that the lengths of the voice bars are compressed, affecting our perception of differences.
What is causing this problem? It's the use of one axis for disparate data. Voice is measured in minutes and texts in units, and in trying to avoid double axes, the designer manages to make things worse by lumping them together.
In the Trifecta checkup, they outlined an interesting question, and collected the right data to address it but the execution of the graphic was wanting.
It's a case of buy one get one free, except that when you go home, you realize you would never buy that second item on its own.
PS. I have more to say about the statistical thinking behind this Nielsen press release at the sister blog.