Secure boot is important. But it can be abused by vendors. Ideally, the computer you bought should belong to you and the vendor should help you keep it secure. But many vendors use Secure Boot to lock out (literally) other vendors and other software from running on your computer. This is not a Good Thing 
. By disabling Secure Boot you’re disabling the encryption keys your vendor installed on your computer. The encryption keys are what are preventing the checks in Secure Boot from passing. In an ideal world your vendor would tell you how to install your own keys to secure your computer, then you would be able to sign any OS you wanted to use. Until then, you’ll have to disable Secure Boot to bypass the vendor restrictions.
Look into Coreboot or Libreboot to see alternatives to proprietary BIOSes.