For the most part, especially where quick turnaround, tactical research is concerned, online methods serve us well.
But, now and again, there arises a need for greater sampling accuracy and representivity – say, for strategically critical studies or ones that will inform major investment decisions. At that point, online’s good enough approach really doesn’t cut it. But the alternative – traditional phone research – is expensive and, in these days of the ascent of mobile, equally problematic.
Or perhaps your need isn’t this dire, but you really need to access a population that is difficult to find through traditional methods – young African American males, recent immigrant Hispanics or the elderly. With current methods, it is both expensive and methodologically stressful to try and get a decent sample in these and other demographics.