It's also a tool for HR to say they have a process that they follow but then still allow all of the decisions about pay increases and performance to be entirely

It's also a tool for HR to say they have a process that they follow but then still allow all of the decisions about pay increases and performance to be entirely subjective. You miss your stretch goals, and so depending on how your manager feels at the time that's either totally acceptable and you're doing a great job, or if they need justification to shaft you then it's totally unacceptable and you didn't do the work well enough to deserve that. Same situation but totally different outcome.