There is no Bitcoin address Necessary a one-time token. Addresses can be absolutely reused. However, for reasons of privacy and security, it is recommended to use a new address for each transaction.
The privacy element has been described in the Bitcoin whitepaper (Section 10):
As an additional firewall, a new key pair should be used for each transaction to prevent it from being linked to a common owner.
The security benefit is that a bitcoin address is a hash of a public key or script. This means that the elliptic curve cryptography used in Bitcoin is corrupted (which can generate signatures) known Public keys), we still have the hashing algorithms (SHA-256 and RIPEMD-160) that help hide the script or public key until a transaction is published. To output the coins associated with an address, the original public key or script must be published. However, if you use a new address each time, the new address will have a corresponding public key or script that has not yet been published. Therefore, it would not be prone to such attacks until you go out to spend.
I would interpret the statement "A bitcoin address is a one-time token." to say that a bitcoin address could be used as a single-use token, and you should not assume that if someone has ever given you an address, that is always the address to pay to him. You should expect that each time there is a different address.
To edit: Yes, reusing the same address offers a lot of convenience, as you do not have to keep track of many different key pairs, and it makes things easier / cleaner if you can send your change to the same address instead of a new one. If you use a new address each time, you can collect many small amounts of bitcoin at different addresses that you can not recombine without linking those addresses. It's definitely a convenience factor.
A persistent address also has obvious advantages. It is much easier to use if you do not specifically request payment from someone. For example, if you wanted to list an address on your website from which you could donate, it would not make sense to keep changing that address. Some people also generate "vanity addresses" (see, for example, Vanitygen) that may have required a lot of work to create, and they may not want to waste this work by switching to a new address.