The drops quick freezing means that some freeze as drops. This makes a rough surface that disrupts the flow of air over a wing or tail surfaces more than smoother ice would do. This, in turn, decreases lift and increases drag. Smaller drops don't contain enough water. Also, the flow of air over a wing is more likely to carry then over or under the wings.
Larger drops create smoother ice because the water runs back before freezing.
This ice can be dangerous, but doesn't disrupt air flow as much. Researchers have also pinned down many of the conditions that create drizzle size, supercooled water drops. These include temperatures from around 14 to 32 degrees Fahrenheit, high humidity, and air that's rising at about 10 centimeters a second. In stratus clouds, air is normally rising at only around one centimeter a second, McCann says. Once ice crystals start forming, they tend to grow at the expense of water drops.