[marcinzm]

Facebook was down for 6 hours last year during the day (in the western world) so that was very impactful most likely. And as wonderwonder said advertising is an eyeballs game and if no one is on the site then they're not seeing/clicking/attributing to ads. Any non-monopoly would have a decent impact from downtime as customers either spend their time on other sites or buy more time sensitive things on other sites.

edit: There's also a lot of revenue impacting things short of downtime especially given the automated and ML heavy paths for most of these sites. A few slightly broken features in a key model can cause a 1% drop in your revenue which for facebook is over a billion a year.