As TDC Nala tried to explain, Walt Disney World initiates this system only at certain locations, only at certain very busy times of the year, and only at peak dining times.
So far - and they started doing this in 2008 or 2009 - there have been no reports of WDW monitoring the counter service seating during
Free Dining... even though that promotion was available property-wide through most of last Fall. This means it likely won't be being used when you're there; even if it is, it may or may not be in effect at the restaurant(s) at which you're dining at the times you're eating there. So, simply because a DISer comes back from a trip and says, "Nope, nobody preventing anyone from sitting down without food" doesn't mean that's an accurate representation of what's going on in every restaurant in every park all day every day.