The last point means that while Netflix trusts these recommendations to be good for them today, if you are looking at this in the future, you should verify that

The last point means that while Netflix trusts these recommendations to be good for them today, if you are looking at this in the future, you should verify that the performance gains are still there for those changes. Perhaps you are running in a system where one or more of these no longer gives a performance gain, or is even detrimental to your overall system health. Trust, but verify.