Many people are otherwise using their ISP's DNS servers, which are often even worse with regards to performance and reliability. Long ago I did tech support for an ISP, and I'd say that 9/10ths of our "outages" were due to our overworked ancient DNS servers failing. I'd go off-script when I took calls during those kinds of outages, and just help people set 4.2.2.2 in their router's DNS settings the moment I saw a strong signal in the line test and hosts not resolving. Managers made snide comments about that not being the official procedure and "not displaying confidence in $ISP", but it fixed the problem.

Because what you get is often faster, more accurate and more resilient compared to the junk DNS run by most ISPs.

And because most site visits start with a Google search anyway.

And finally, because I am comfortable with their privacy statement : https://developers.google.com/speed/public-dns/privacy

I live in New Zealand where all the ISPs and mobile carriers provide fast and reliable DNS resolvers. I've looked into switching to alterntive DNS providers but every one of them are slower than my ISP's resolver. I'm aware that the sitation is quite different in the US and certan other countries, but I wish more Americans were aware that junk ISP-provided DNS servers seem to be an issue exclusive to certain countries (such as the US). I think it would be an intrerestin exercise to figure out why they occur in certain countries and not in other countries.

Sorry - I should have been clear. I am from India - and the ISPs here are quite bad. I have no idea about the USA ISPs.

Because in certain countries the ISP has to respect the legal regulations and so the DNS server provided/defined by each provider will block/redirect certain web sites. These could be torrent trackers, subtitle distribution sites, political and/or religious sites and so on... In some parts of the world alternate DNS servers allow people to access all sites :-)

Not to mention that some ISPs redirect users to pages full of ads when a domain doesn't exist or use DNS to MITM users and inject ads into pages.

I use it because I'd rather tell Google than my government, which is not on friendly terms with either US or Google.

I’m curious. What DNS server do you use? Or do you just memorize the IPs of the websites you want to visit? :P

you can run PowerDNS Recursor locally (or any DNS non stub resolver).

it's not that slower.