Thank you for the replies. Even after reading, I still do not understand the benefit of locking the drive to a computer. Is file vault encryption not good enough?
FileVault implemented in the kernel can’t completely protect the encryption keys. It’s difficult, but wouldn’t be impossible to extract the keys from RAM if you take control of the kernel. And it requires overhead on all reads and writes on the CPU, as well as duplicating the encryption standard SSDs also perform (that mostly just means you can’t read the raw NAND if someone smashes the SSD controller). As SSD performance increases, this overhead becomes more noticeable.
The T2 takes the load of FileVault away from the CPU, which improves performance, and avoids the double encryption overhead of FileVault on standard SSDs. But the big security win is that the keys when FileVault is enabled shouldn’t ever wind up in RAM, or ever leave the T2 chip. Making it even harder to extract the keys. On top of that, instead of “merely” generating an AES key from a password, which means you can brute force the password of a regular FileVault partition, the final AES key is a unique AES key from the T2, entangled with the password you provide.
Overall, it provides protection against brute forcing against weak FileVault passwords, and makes it so that an attacker can own the kernel and still have the encryption keys kept out of reach.
The cost is that the encryption keys can’t be re-generated on boot/login without that EXACT T2 chip or some very expensive AES brute forcing. But that’s partly the point.
BitLocker works in a similar way, where the TPM is used to house the encryption keys. The difference is that you can generate a recovery key which is a sort of special encryption key that can be used to bypass the TPM and read the drive in situations where you forget your password or the TPM fails.