Enabling tokens allows DDEX users to trade ERC20 tokens for WETH directly from their wallets.
There is no withdrawing or depositing on DDEX: all tokens stay in your wallet until a transaction completes, and WETH is transferred instantly to the seller's wallet upon completion. To allow this type of interface to occur, users must "enable" a token to sell from their digital wallet.
What is "Enabling" a token?
Simply put: "enabling" a token type allows DDEX to facilitate exchanges of that token in a user's digital wallet. It does NOT mean that the user is giving full access of their tokens to DDEX - it only gives DDEX an allowance permission to facilitate transactions on the user's behalf.
Enabling a token is a one-time transaction after which the user can freely sell this token type from their digital wallet on DDEX forever.
Note that even with this permission DDEX still cannot do anything with tokens in a user's wallet without an additional approval signature!
Why do I have to Enable tokens to sell them on DDEX?
ERC20 Tokens cannot be traded from your wallet by an exchange without obtaining both an approval and allowance from the wallet owner. This is a security feature of ERC20 tokens. So there are two transactions that a user must approve in order to sell their tokens on DDEX.
What are these two transactions exactly?
First, the user must enable the token for sale - setting an allowance for DDEX to trade that token on their behalf. This transaction is a one-time transaction: rather than requiring a user to sign two transactions every time they wish to trade, after signing it once the user is enabled to sell that token on DDEX forever. This transaction requires accessing the Ethereum Blockchain, so you will need to specify a gas price for it through your digital wallet interface (i.e. a MetaMask popup).
The second transaction contains the actual specifications of the sale (the limit price and amount of tokens). When you place a limit sale on DDEX, you will see an additional signature popup through your digital wallet interface - however this one does not have a gas fee! No gas fees are paid on sell orders until a transaction actually occurs. This is actually a pretty nice feature: users can cancel and resubmit sell orders that are not filled as many times as desired without paying a gas price.