UNIX for Advanced & Expert Users

Why is root, by default, a member of some system groups? I can't see any reason for this. Root has permission to everything and adding root does not give the group any more permission, so what's the point?

Here is part of my /etc/group file from a recent arch linux system. Notice that root is a member of bin, daemon, sys, adm, and disk. Why?

Code:

root:x:0:root
bin:x:1:root,bin,daemon
daemon:x:2:root,bin,daemon
sys:x:3:root,bin
adm:x:4:root,daemon
tty:x:5:
disk:x:6:root
lp:x:7:daemon

I've been programming unix and linux for maybe 20 years and this sounds to me like a simple basic question but I just can't find an answer.

Thanks.

Moderator's Comments:

Please use next time code tags for your code and data

A wild guess is applications or scripts checking for membership of those groups. Maybe those programms are no longer in use but the file was not cleaned up in some distributions.