Well, I mostly found it interesting because it shows your digital footprint and Google's panopticon so eerily well. Even when I thought I had most of the privacy settings turned to paranoid, I still have more than 400 items a day on that activity log just from using Chrome and using an Android phone. I, for example, didn't know that Google stored the amount of times I looked at Whatsapp. I don't really understand why they or any advertiser would care.
Every time you open an app it's an opportunity to get you to look at something that might make you buy something later on down the line. Regardless of whether or not that space is being used for advertising, it displays a trend in behavior. I don't really understand why they or any advertiser would care.