Where is it usually used? Where can I read about it, and other often used groups?
base-passwd package guarantees the presence of certain users and certain groups in a system. The documentation is in
/usr/share/doc/base-passwd/users-and-groups.html) (source available online in Debian Salsa):
bin HELP: No files on my system are owned by user or group bin. What good are they? Historically they were probably the owners of binaries in /bin? It is not mentioned in the FHS, Debian Policy, or the changelogs of base-passwd or base-files. LSB 1.3 lists bin as legacy, and says: "The 'bin' UID/GID is included for compatibility with legacy applications. New applications should no longer use the 'bin' UID/GID."
So, it's part of the LSB specification, and since Debian used to aim for LSB compliance, Ubuntu has a
bin user and group.