Keeping Time Synced Between Machines in a Data Center

Earlier this year, i saw a facebook released in open source hardware implementation of a time card that contained a miniature atomic clock chip. They presumably used this to keep time synchronized between servers he data center. Do you feel that tightly synchronized clocks are necessary? Are they worth the effort of having customi software? Or can we just deal with the clocks differing by a certain amount? I've not a fan of expensive, high resolution clock hardware. You can do perfectly well with different machines that have slightly different clock speeds and line them in software. Yes.