Binance or Coinbase are exchanges which can be used to switch between cryptocurrencies. Such exchanges are centralized – being both the custodians and intermediaries of the traded assets.
These exchanges do not allow their users to fully control their assets in a bid to reduce their risks of getting hacked and preventing mismanagement.
With decentralized exchanges, this issue is resolved by permitting the exchange of cryptocurrencies while still holding custody of your coins.
Since no funds are stored on centralized exchanges, there is no need for users to hope that the exchanges will remain trustworth with their funds.