The bubble chart is one of the most hopeless data graphics ever invented. It is sometimes useful for conceptual charts but trying to express data with it is a lost cause.
The Wall Street Journal used a bubble chart to show the trend in whistle-blower lawsuits in the U.S. The original chart looks like this:
Focus on the top part of the chart. Now apply the self-sufficiency test (link), as follows:
First, cover up the data labels. You'll notice that no information is conveyed by the bubbles in and of themselves.
Second, give yourself a hint. The size of the first bubble corresponds to 363 suits. What does that tell you about the second bubble? Unfortunately, the answer is still nothing.
Third, give yourself two hints. The second bubble from the left has size 311. Now try to estimate the size of the rightmost bubble given those two pieces of data. This exercise is still extremely taxing.
Thus, the conclusion about bubble charts is:
That is to say, it fails the self-sufficiency test (link). The chart cannot exist without the data labels. The graphical elements do not provide any additional value.