Free Run: Your "clock" keeps running all the time and does NOT stop at tape stop
Record Run: Your "clock" starts & stops at tape start/stop & stamps the tape running time
I've used free run when we've had multiple recorders & set the time at local time of even GMT time. Also used free run with local time in doing documenting & testing NASA "thingies"
Free run is great for multi-camera shoots. You set all of the cameras for "time of day" timecode so that they all are on the same time. That way, syncing up your footage becomes much easier.
Record run is better for a multi-day shoot where you set your timecode to start with hour 1 on day 1 of your shoot, and you basically keep track of your shooting sequence. This way, you always know what was shot first, you can keep track of your takes, etc.