I always had to document and explain why I thought an employee deserved a raise, or should not get a bonus, etc. Even as a director with ~20 reports I don't have unlimited firing power and I still need to regroup with HR when it comes to that.Having that system in place isn't enough. You need that system to have teeth, and you need to have someone with as much power as you who will review your decisions and play devil's advocate.
In many teams I've seen with documentation and HR hurdles, they're not real hurdles, they're just there so that there's a paper trail at all. That's because:
1. Most people in the company including the manager's boss and possibly even most teammates of the employee don't see enough of the employee's work, so it's often the manager's word vs. employee's. A bad manager will exploit that, intentionally or unintentionally.
2. When in doubt, the management hierarchy tends to side with the manager on things, because they by default trust the manager more than the employee and their view of the facts of the situation usually comes from the manager. A bad manager will intentionally or unintentionally editorialize the facts on their way up the hierarchy.
3. HR tends to avoid making waves. The only time I've seen HR (excuse the metaphor) plant the flag on the hill they intend to die on, it's because the person being fired or managed out was a protected class of worker. I have never seen HR push back just because the manager had insufficient reasons or suspect reasoning. A bad manager will just shove decisions through HR, intentionally or unintentionally.
In all of those places, there were systems in place where managers had to document those decisions, but there wasn't real accountability, so the systems were nominal at best.