I championed the institution of a permanent check-in partner system at my current place of employment after seeing it used intermittently at my previous one.
Unlike pair programming, it’s extremely easy to get people on board with it. It rarely amounts to more than about 3% programming time investment (assuming a day’s work and a 15-minute review).
The obvious benefit is that bugs get caught before check-in, but I believe that the distribution of knowledge that check-in reviews promote is a more important benefit in the long term. Check-in partners learn good techniques from each other, maintain coding standards, and learn what code is actually going into the project.
So far, at my current shop, everyone who’s been introduced to the idea likes it, which is pretty remarkable for a piece of process.