In multifocals different parts of the lens (e.g., concentric rings) focuses images from different distances onto the same part of the retina. This necessarily means less contrast (focused image superimposed on blurred image).. As I get older I seem to crave more contrast. Maybe that's why, when I tried multifocal contact lenses briefly, I didn't like them, and stuck with monofocal plus reading glasses. I use bifocal glasses over my contacts when flying.

See, e.g., here for more info:
http://www.allaboutvision.com/contacts/bifocals.htm