Encrypting your wallet is crucial because it adds a layer of security to your Bitcoin holdings. Without encryption, if an attacker gains access to your file system, they can instantly spend your coins since the sensitive wallet.dat file, which holds your BTC ownership, remains unprotected. Encrypting the wallet with a strong passphrase acts as a lock, preventing anyone who doesn’t have that passphrase from utilizing the funds even if they access the device or file system.
The risk of not having a password or encryption is that anyone gaining access to your computer or the wallet file can freely spend your Bitcoins. Encryption acts as a barrier, requiring a passphrase to access and use the funds, thus significantly reducing the risk of unauthorized transactions or theft in case of a security breach or unauthorized access to your system.