As a former Kindle developer, I can say that most of what's mentioned in this article are metrics used to understand how the features are used (bookmarks, highlights, dictionnary, etc.), how much they are used, and in which country. This allows the teams to focus on features that are actively used, and sometimes lead to discontinuing features that see little to no use. Hope that helps.
Understanding how the book reader features are used in practice is good. Selling the same data to a advertiser is bad. Profiling people into predefined groups is bad, and the technology has risk of having false positives/negatives that reinforce stereotypes. The law has yet to catch up to treat information gathered by libraries and information gathered by a developer of e-readers as being very similar in risks.