The DNS (Domain name System) servers offered by third-party companies like Google, can be faster than the internet service provider that’s why we recommend using third-party DNS server, a big advantage of using third-party DNS service is faster web browsing experience and security
After using a third-party DNS system, you can change your domain name system in your Wi-Fi/Internet settings. you may see some significant improvement in your Android’s Internet speed and functionality, especially ISP (Internet service provider) DNS is not satisfactory to you.
The advantage of Using Third-Party DNS
Phishing Protection – OpenDNS performs filtering to block phishing sites. Modern browsers have built-in phishing protection already
Better security and More Reliable
Speed Improvement – It is not guaranteed that using third-party DNS your internet speed will be increased but it depends on ISP’s DNS servers but in most of the cases third-party DNS server can be faster than ISP’s DNS servers.
Parental Controls – If you have children who have access to your Android phone or laptop/computer, you can create a parental block on specific websites that may not be safe for them. By using a third-party DNS service, you may have more parental control settings than offered by your Internet service provider.
Access Blocked Content Or Bypass Web Censorship – Some ISP block websites through DNS level, if the website is blocked this way (DNS level) then you can unlock by using third-party DNS or with changing your DNS server to a third-party DNS which doesn’t block the site. This won’t always work if your website is blocked with IP method then you can’t get access with changing of DNS.
I think if your ISP’s DNS servers are working fine for you, and you aren’t trying to do some region block dodging, then just keep using them. Using a third party DNS server means one more entity knows all the websites you visit. If you aren’t that overboard about privacy then that doesn’t matter for you.