Earlier quoted context omitted.
What pushed me into using it was when comics.com (now gocomics.com; the official online source of a number of syndicated newspaper comics) had ads that would -minimize my browser-, display a pop up designed to look like a Windows system warning, that advised me to download some malware masquerading as a virus scanner.
Gocomics.com is a particularly good example - I find it surprising that they appear to accept such low quality (one weird old tip) and shady (download now/you have 1 new messages/etc) ads.
As someone with a browsing profile that isn't targeted by those kind of ads, I've found out second-hand that I've been running ads like that a few times. Trying to prune specific ads is an endless game of whack-a-mole that I've never been able to win, and disabling an entire category of ads just to prevent 1% of them from running is very tough on the bottom line.