I guess the theory is if you water for short periods too often it encourages short root growth because the plants don't have to strain to reach water. If the water system fails for a few days, some damage can be done.
On the other hand, watering for longer periods less often encourages the plants to strain their roots a bit to look for water deeper, so they are better able to withstand an interruption in irrigation...
At least that's what the "experts" told me. I'm still a novice on this and just a home gardener.