Token approvals are among those DeFi mechanisms which appear rather harmless until it becomes clear what they allow.

While using a decentralized application, the user gives a permission to some smart contract to spend some tokens from his or her wallet. Depending on the type of approval, the permission will be valid long after the initial transaction.

The key point here is that while approving a token, the user does not necessarily transfer it but provides a spending permission to a certain contract. In case of vulnerability or malice of the contract, this approval may make the user's token balances prone to some risks.

Cancelling all previous approvals each time after completing a transaction may also be an inefficient way. Such action may take additional transactions and gas costs, and the user will have to approve the token once again upon revisiting a protocol.

Thus, what is needed is the understanding of the permissions provided prior to the signing.…