What is the wheel user group for?

Quoting from this superuser answer by Rich Homolka:

Mac OS X has roots in BSD UNIX, a.k.a. the UNIX that came out of UC Berkeley. They had a group of trusted people that could become superuser by using the su command. So they coded their UNIX to only allow people in this specific group to become superuser using su. They chose the groupname 'wheel', supposedly reference to other systems that had WHEEL, possibly a reference to being a 'big wheel'

It's less important now that you have the GUI authorization popups and sudo. You can use sudo without being in wheel group I believe.

From Wikipedia:

Modern Unix systems use user groups to control access privileges. The wheel group is a special user group used on some Unix systems to control access to the su command, which allows a user to masquerade as another user (usually the super user).

In computing, the term wheel refers to a user account with a wheel bit, a system setting that provides additional special system privileges that empower a user to execute restricted commands that ordinary user accounts cannot access.The term is derived from the slang phrase big wheel, referring to a person with great power or influence.