Centralized vs Decentralized

CENTRALIZED.
Centralized exchanges can be used to conduct trades from fiat-to-cryptocurrency or vice versa. They can also be used to conduct trades between two different cryptocurrencies. While this may seem to cover all of the potential transaction types, there is still a market for another type of cryptocurrency exchange as well.

DECENTRALIZED.
Decentralized exchanges are an alternative; they cut out the middle man, generating what is often thought of as a "trustless" environment. These types of exchanges function as peer-to-peer exchanges. Assets are never held by an escrow service, and transactions are done entirely based on smart contracts and atomic swaps.

SECURITY.
The big difference between decentralised and centralised exchange is security. Decentralized Exchange does not keep your funds. We have centralized institutions in traditional financial system. These institutions can be robbed, hacked or corrupted. Using of a decentralized exchanges gives us opportunity to keep control of our own keys to our own funds.