You don already explain wetin centralized and decentralized exchanges be so from your explanation, person suppose know say decentralized exchange dey give you full control over your coins while for centralized exchange, no be you dey control your coin as anything wey centralized exchange go still affect your coin.
For people wey wan change their money to their local currencies, centralized exchange na the best option because dem dey charge smaller money than decentralized exchange but for people wey wan save their coins, make dem use decentralized exchange because na for their their coins dey safer.