Well I use it (and I assume most people use it) because I don't want to see ads. Advertising on the web is largely just obnoxious, ugly, and crude. Also the relentless tracking is a little creepy, so there is another small benefit to using an ad blocker.

I know there are some small groups trying to do good advertising on the web but it is so insignificant it doesn't even register. Large and important websites don't care enough to curate their advertising (or won't curate it to an acceptable level because of the financial hit they'd take), it is a lost cause.

The worst part is that this shit-show is steadily seeping into the mobile app ecosystem, at least on Android (I'm not on iOS enough to make a judgment). I don't know how many times I've seen beautifully designed apps with a damn ridiculous yellow flashing banner (etc) shoved in the middle of it. And 99% of the time there is no option to pay for a version of the app without advertising. I get why people do this (gotta pay the bills, Android users won't pay for apps, etc) but it sometimes seems like people don't take any pride in software anymore. :(

In contrast, I was quite surprised with how pleasant the advertising is on my Kindle. I suppose that can be a benefit of having a closed ecosystem and a device with limited capabilities.