I've downloaded a Bitcoin Core, why it's recommended to use a new address for a new transaction?
Refreshing address with every transaction keeps your identity more intact as It can't be refereed with any other transaction as the address is new.And it is good for future perspective as when coins are sent to an address, they're sent to RIPEMD-160 of sha-256 of the public key. In order to spend it, you reveal the public key, and then sign with the corresponding private key. Thus, if at some point in the future someone discovered a weakness in ECDSA that allows deriving the private key from the public key.It will be safe as you address is changing so the new public key will not be in the blockchain and it will be not vulnerable.