Everyone prefers to determine the flight status before going to fetch or drop the passengers to the airport. This exercise saves the time as you do not have to keep waiting endlessly for hours, in case the flight is delayed or cancelled. But, if you go strictly by the flight status information, then you might still reach either too early or a bit too late. You might believe that there is some problem with the data aggregators who provide this information but that may not be so. It could be a deliberate act of not telling the accurate flight status till the time the flight has landed at the airport.
After the flight booking is done and the flight has taken off, there could be lags or leads in the in-flight information. This is done specially for the security reasons where there is a danger of this real-time information being used by enemies of the state or the terrorists. When flying over or around the war prone areas or over the territories controlled by enemies, the correct flight status information could be a security risk for passengers.
So, if you are going to the airport to fetch your near and dear ones, then it is better to still arrive a bit early, if not too early. Similarly, if you have to catch the flight, it is better to be at the airport well before the time of arrival for the same reason. If you have the flight route over or around the countries which are war prone, then there is good chance of correct status not being provided.