There are several threads already about the comparison or on the talks between centralized and decentralized exchanges.
https://bitcointalksearch.org/topic/centralized-and-decentralized-exchanges-5104208
https://bitcointalksearch.org/topic/centralized-exchanges-vs-decentralized-exchanges-5165454
On topic, the main difference between the two excluding the privacy thing is that centralized exchanges do have fiat pairs
and thats the main reason why anyone do end up on using cex and we can actually see the difference when it comes to volume or liquidity.