Because race conditions are so hard to detect, the race detector is obviously prone to false negatives. Just because the tester doesn't find any race conditions doesn't necessarily mean that there aren't any. But the race detector never finds false positives. If it finds a race condition, that condition is very real.
You could just run your app with the race detector on all the time, but there is a performance cost to using the race detector.
One way to get around this in cloud/clustered environments is to deploy your app on a few machines with the race detector on and the rest with the race detector off. That way you're running your app with a production load and you're more likely to find race conditions, but you'll mitigate the performance costs associated with the race detector.