The concept of logging information about your daily life has been around for decades. According to Wikipedia the idea of doing this with wearable devices dates back to the 70s, but of course the technology was not up to it back then.
I'm actually not that into logging my daily steps and how I sleep. I don't have a Fitbit, but I do have the Google Fit app on my phone. I just don't check it that often. I have the Endomondo app too as that gives me lots of stats when I go running, so I can see just how slow I was.
I do like logging information so I can look back so see what I was doing. My biggest dataset is probably on last.fm which has been logging what I listen to for over 12 years! This site was formerly known as Audioscrobbler. Many music apps have this logging build in and it can be added to others with plug-ins. I have one in Chrome that logs music I play in Youtube, Bandcamp and other sites with music. It's on my phone too, but hasn't been logging my podcasts via Pocket Casts in a while. I'm more interested in the music anyway. I can see that Eels, Bjork and Radiohead top my all-time listening, but more recently there's a lot more prog.
I love that last.fm does its thing automatically. Other services require manual logging. I've used various sites to log my reading, including something that ran on my own site, but these days I use Goodreads. It's useful to have to social aspect to see what friends are reading. You can log books by scanning the bar codes. I'm not reading as much as I'd like due to lack of time.
At times I've logged every time I filled up the car to check the economy, but I've given that up for now. I was logging stats like follower count from various social sites, but Steemit has that anyway via SteemWhales. I guess I could access a list of every post I read or voted on here on Steemit. There's another set of data. I really don't know what I will do with it all, but I could go back to a given day and see what I was reading and listening to then. Can probably create some pretty graphs too. I do plan to play with the API at some point. None of this is essential, but some of us like the stats.
Much more at Lifelogging and Quantified Self