Almost every dApp needs a user's authentication to send a signed transaction to the blockchain. From minting tokens to making a simple transfer, users must always sign their transactions whenever the client-side application needs to call a SmartContract method that requires the user's Account.
Signing a transaction means that, without a solution like WalletConnect's integration, the user would need to trust his privateKey to the dApp. For obvious reasons, outside of testing environments, this is a huge security issue, as the dApp could simply use it maliciously, stealing funds or signing something not approved by the user.
From a security perspective, providing your key to an application is a HUGE risk. WalletConnect mitigates this risk by delegating all transaction signing operations to the user's wallet. Applications are instead given the ability to communicate directly with the wallet to request user's signature.
WalletConnect is an established solution to tackle this issue, and it's already used by many dApps and users.