In the late game, when youve already got plenty of creatures, it helps finish the game by making your entire team larger and giving them vigilance so you can freely attack without worrying about dying on the crackback
A five mana 4/4 is nothing to write home about, and +4/+4 is quite a big bonus when it enters the battlefield, but in a format full of Nissa, Voice of Zendikar and Gideon, Ally of Zendikar, chump blocking is a pretty normal occurrence
While having to actually deal combat damage to trigger an effect could be a restriction for some creatures, Hellkite Tyrant has both flying and trample, which all but guarantees that its swing gets through to an opponent
The world nurtures your creatures by letting you cast them, which nurture the land in turn so it taps for more mana and both flourish in harmony with each other