Random ventilation (in addition to being extremely energy inefficient) provides ventilation in random amounts, at random times, from random locations, at random temperatures and of random quality. The amount of ventilation literally changes with the breeze and the seasons, in a manner completely unrelated to what is actually required. Relying on random ventilation is “gambling” with indoor air quality and your family’s health.
“Tight” houses are never “too tight” but they have been often “under-ventilated.” “Tight” houses are the only houses which CAN be ventilated in a controlled manner. Leaky houses often leak so much air of questionable quality that a mechanical system is overwhelmed.