If Google is like Facebook in this respect then a senior engineer who "meets expectations" in a performance review stands to make at least 15-20% of their salar

If Google is like Facebook in this respect then a senior engineer who "meets expectations" in a performance review stands to make at least 15-20% of their salary as a bonus. If you get below "meets expectations" you are probably going to be fired very soon. Hence your "meets expectations" bonus target is essentially no less guaranteed than the base compensation you would also lose out on if you were fired. The bonus target at companies like this is not an "above and beyond" bonus. There are bonus multipliers (and potentially non-standardized discretionary equity bonuses) for higher than expected performance.