It doesn't, monitoring and configuring battery saving is relatively harmless to the majority of consumers. The point that the OP made is that there is nothing stopping them from doing more harmful tests like experimenting with web traffic, running benchmarks or something, tracking app usage in terms of direct relationships (e.g. this person always reads emails, then hacker news, then checks snapchat, then browses these kinds of shopping apps), etc. I'm not saying that these are likely, but when information about specific users drives ad revenue up then it's not much of a leap to suggest they'll collect a bunch of information that people don't want them to collect.
> I fail to see how ad revenue and data collection has anything to do with battery saving mode.
The implication is clearly that someone whose revenue is based on prying on your personal information has more incentive to do things like this than someone whose revenue is not affected by how much they know about you.