The loss of time is minimal for small distances (< 500km) as you don't have check-in and don't have to travel to the airport first.
For longer distance flights: Wake up at 07:00, take the train to the airport at 08:00, take the 10:30 flight from Schiphol to Barcelona and get out of the airport at 15:00. Take a taxi to the city center and arrive at 15:30. Or take the 08:00 train, sit back, relax and get off right in the center of the city at 20:00. You have may lost a couple of hours but you could sit down and read a book the entire time. Luggage is easier. Nobody groping you or giving you troubles about fluids. And good food in the trains too.
Ever better: Night trains. Take the 21:00 train. Fall asleep. Wake up at 09:00 having passed two countries.
For longer distance flights: Wake up at 07:00, take the train to the airport at 08:00, take the 10:30 flight from Schiphol to Barcelona and get out of the airport at 15:00. Take a taxi to the city center and arrive at 15:30. Or take the 08:00 train, sit back, relax and get off right in the center of the city at 20:00. You have may lost a couple of hours but you could sit down and read a book the entire time. Luggage is easier. Nobody groping you or giving you troubles about fluids. And good food in the trains too.
Ever better: Night trains. Take the 21:00 train. Fall asleep. Wake up at 09:00 having passed two countries.