Its a spectrum, like all things. It crosses from everyone has the keys like in this example, to centralising a signing service using just software, or using so

Its a spectrum, like all things. It crosses from everyone has the keys like in this example, to centralising a signing service using just software, or using something like KMS or CloudHSM, or YubiHSM, or going big and getting a HA Luna (or similar) HSM setup.