High pressure. People get fired if they under perform, and under perform may not be what you expect it to be. Employee evaluation is mainly "impact" based - meaning you have to show measureable product impact every half.
This creates insensitives for people to produce low quality code, and under-maintaining it, since you are better off solving 90% of the problem and say you're done without covering edge cases.
This also pressures people to work alone on highly measureable projects and not share the credit for larger projects.
in the year and a half I've been with the company, I've seen 4 people fired in a 30~ person team, plus two more quit ahead of being fired. On other teams, however, I've seen people rest-and-vest for years, so it's probably very dependent on the team and managers.