Why use Pd-extended when Pd Vanilla already exists?Up to Table of Contents
It provides a standard platform for people who want to use any of the included libraries. If you are using those libraries, then you know they'll be in the same place on all platforms and all installs if you use Pd-extended. If you rely on the user installing the libraries manually, then there are no guarantees how the libraries will be setup and installed.
Note: Pd Extended is abandoned, see https://puredata.info/docs/faq/ispdextendeddead