Smaller prints are engaging, feel special, are more intimate. But when I was at college doing photography the 'small dark print' reigned supreme. I think the main thing is the smaller print forces an engagment with the viewer by making sure they get close enough, whereas a larger print can be seen from the other side of the gallery, but if there are fine subtleties these can be missed because the viewer already thinks thay have 'got it'.
But printing large is now a fashion and, depending on wall space available, it can work. The main thing that bothers me about very large prints is the feeling some are very reliant on simply being large for their impact, forgetting that it should be a good picture as well. And too many photographers are drawn into offering large prints for sale, as if people will think they are getting more art for their money, especially with the rise of inkjet printing. Yet all too often the potential buyer will have a small bit of wall to devote to a picture, and may want to collect more than one image by the artist. It's something Ansel understood.