This. And thats exactly my case. You have a deadline and you just commit to that. We as a team always "judge" or analyze in a constructive way our own job, we are adults and we know our flaws and our strenghts, once we delivered a job we ask ourselves what could we've done better, etc. So there's no need of corporate bullshitism and arbitrary reviews.

How do they ensure that rewards (promotions, salary increases, bonuses) go to people delivering value to the business and not those who are friendliest with management?

Yes they are. In fact, one’s performance objective in many cases depend on effective teamwork with one’s peers. And then there are the behavior part of performance reviews where you’re graded on intangibles like teamwork, trust-building, etc…

Performance review systems will always have flaws, but it’s better (in nearly all workplaces) to have a formal and transparent process for them than to have none at all.

I once saw a book written by a former HR manager who states, performance reviews are not really used to get better performance. They are ways for organizations to get documentation to fire you without getting sued for it, if they need it. HR’s job is to protect the company, not to protect the employee.

Yes they're valuable. Working together with your team is a core skill that everyone needs to have to be a professional developer, and as such is a major part of the reviews I do. Any good leader will encourage cooperation over competition.