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.