https://wiki.debian.org/DebianUnstable
Debian Unstable (also known by its codename "Sid") is not a release, but rather the development version of the Debian distribution containing the latest packages that have been introduced into Debian. It is not a "rolling release", as no release-like quality assurance and integration testing is done on it.
You need some amount of testing because packages do break, the 2 week testing window on arch is really important in making sure your pc can at least boot.