Peering out from under my tinfoil hat for a moment, I'm not *entirely* sure I do, not least is because the aggregated data from millions of android phone users like me is actually useful to those users as well as advertisers.
Ever wondered how google knows where traffic jams are located, or why sometimes routes get changed on the fly?
But at the same time I hate giving my personal data away, which is why I went through my Xiaomi phone when I first got it, turning off and disabling apps & tracking, access to contacts etc. When Chris's Redmi Note 5 arrives (her Lumia 650 is becoming unreliable and the battery only lasts a day or so) in the next few days we'll need to do the same for that.
If you want to check to see whether you've been bleeding data without knowingly allowing it then wander over here. iOS users - this may apply to you too, if you have ever used any services from Google. I was pleasantly surprised to find all my tracking settings switched off, probably thanks to being scrupulous with the Xiaomi, with the exception of youtube content which is useful occasionally (they suggest good videos far less often than one might expect, although there's recently been a run on Marina Sirtis comicon appearances that had me chuckling - she's a real Lundun gel wiv a right norf an sarf).
I almost wish my phone had a sandbox mode, for openly sharing stuff that doesn't matter like location when using maps, and a private mode that locks away contacts etc so that applications which demand access are unable to filch the stuff they have no business sharing (why does an audio recording app require access to contacts?)
And while we're mentioning phones, my Xiaomi 4X did a recent OS update at the end of last week that made it go all slow for a few days. It was getting to the point where I was going to see if there wasn't some way to step it back when suddenly it became all snappy again. Weird. I miss the better wireless performance of the Lumia 640, but I don't miss the apps that didn't work, laggy performance and short screen-on time. I suspect a large part of the excellent standby battery life of the Lumia was simply because the aerial system was very good, and the phone used much less power hunting for a weak and difficult signal. Other manufacturers might learn a lot from the Lumia people.