Here is an article about synchronizing recording devices so that there is a common time reference for all machines and people involved in a recording project involving either just audio, or both audio and video. In the days of tape recording (and for those who still use tape) it was common to "stripe" the tape with SMPTE (Society of Motion Picture and Television Engineers) time code, essentially using up one of your precious available tracks, for the sole purpose of providing the common time reference, which was really handy if you were using several MIDI instruments.
For many of us recording on our computers, this is not as necessary anymore. And a lot of us will never use it, especially those of us recording solely for voice-over applications. But it is always good for the recording enthusiast to understand other aspects of the game. See the article by Brent Hoover here: http://www.prosoundweb.com/article/synchronization_and_timecode_basics/