In a distributed ledger, every transaction is recorded publicly. Public verifiability allows anyone to verify correct system working.
Everything is a archived and authorized in a decentralized way and then system ensures that data is processed in a reliable and transparent manner.
A third party cannot make any changes to the system.
With no central point to be exploited the system is protected against hacking, attacks and fraud.
Peer to peer and business to business transactions is completed without the need for third party that odds costs.
Completely new business models that blockchain introduces may lead to substantial competitive advantages.