[mjg59]

You should be able to do what you want to it. You should also be able to configure it such that only you can do what you want to it, and nobody else can.

Secure Boot protects against boot kits, malware that replaces the bootloader and backdoors the OS as it boots and before any other security protections kick in. Real world bootkits have been found in the wild, and we've even seen them use vulnerabilities in signed (now revoked) bootloaders, so we know secure boot has forced their developers to work harder. You may not be worried about that as a risk (well, until you are) but there are real people who this has genuinely protected.

Is it worth it by default? Completely reasonable separate discussion to have. But is there a reason it exists? Absolutely.