An address book is a digital tool that stores the addresses of other users or contracts you send transactions to or interact with. This tool is a very powerful tool and can play a very vital role in security & verification.
For instance, there is malware called clipboard hijacker. This malware attacks your clipboard, and anytime you copy a crypto address and paste it to send funds, it changes it to the hacker's address which is not yours. This malware has been discovered to monitor more than 2.3 million cryptocurrency addresses and is responsible for millions of stolen funds. This malware is common with PCs and can be an issue when using the MetaMask extension with AirGap Vault.
The address book also improves security in this area. By storing addresses in the address book, users can avoid the risk associated with such malware or falling victim to phishing attacks when interacting with a smart contract. Ultimately, this prevents users from accidentally sending funds to the wrong address, which can result in a loss.