It’s an option for payment. Detailed on the same link:
> Storj created the STORJ utility token as a medium of exchange on its decentralized cloud storage network. The STORJ utility token facilitates payments from people around the world for their use of the Storj network to store their data, and Storj uses it to pay our community of Storage Node Operators that rent their unused hard drive capacity and bandwidth to the network.
> Storj created the STORJ utility token as a medium of exchange on its decentralized cloud storage network. The STORJ utility token facilitates payments from people around the world for their use of the Storj network to store their data, and Storj uses it to pay our community of Storage Node Operators that rent their unused hard drive capacity and bandwidth to the network.