>All that will happen is that one second your computer will think it's on time, and a couple seconds later your computer will think that it's a second behind and correct itself against the NTP server.
The problem here is that not all systems adjust at the same rate. So once all the systems are a second off, they will all be slightly out of sync with each other as they skew their clocks until they're all correct again.
For us, clocks being under a second out of sync is not a big deal. But for software that has to be well synchronized between hosts, it's a huge deal. So it's better to do it Google's way to keep their infrastructure working reliably.