I installed an adblocker on my Mac after I was using mobile tethering with my computer muted, and some ad went through a huge video playlist in another window using close to 1 GB of data. It was worth around $20 at the time in local currency, and that was it for ads on the laptop.

I installed a hosts blocker on my Android phone after I found myself hitting a large number of sites which would popup ad alerts and then forcibly redirect to another site (where they'd try and get me to download and run an APK). This might be more prevalent in "poor" countries where the fill rate is bad, and so these kinds of scams end up being the only ads available and possibly aren't noticed by the networks.