The Wither rank unlocks the following!
/skin (Change your skin in game)
/nick (Change your display name in game)
/hat (Put any item on your head)
Custom text + fonts
/echest (Access your ender chest with a command! No need for an actually ender chest now)
/afk (go afk to auto farm, don' get kicked for inactivity, and more)
A cool tag before your name!
Plus more to come!
Plus buying this rank helps keep the server online and paid for :)