There are many methods to block unwanted outgoing requests. Examples include browser settings and extensions, and .hosts files. While DNS blocking won't affect direct accesses to a numeric IP address, it can be easily implemented to block entire domains and their subdomains, for an entire network as opposed to app-by-app or device-by-device.
Philosophically, DNS may not be the place do do such blocking, but it can be very effective, especially as part of a defense-in-depth strategy. What additional advantages and disadvantages are there to blocking with DNS?