I've downloaded a Bitcoin Core, why it's recommended to use a new address for a new transaction? I'm a bit new to Bitcoin.

I just downloaded a Bitcoin wallet "bitcoin core". And I have downloaded all the nodes (a lot of data, I believe it's the complete one).

When I click the "Receive", I can request money.

But I noticed that every request, I'm assigned a different address. Then I noticed that it's an official recommendation by the software.

Is there any reason for that? How many addresses can I have? What do I need to be prepared if I have a lot of address? (for instance, to backup something)
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.