It doesn't seem to have harmed the plant, but it is unsightly. It is possible that your F. benjamina is infested with soft scale insects or mealybugs. Both of these sucking insects excrete honeydew when they feed on the plant sap. However, Ficus could produce a sticky substance without insects feeding on it, so inspect your plant closely.
Mealybugs are easier to see because their bodies are surrounded by white cottony tufts of wax.
Look for mealybugs on the undersides and axils of the leaves, shoot tips, and the crevices of stems or branches. They are often at least an eighth of an inch long. Mealybugs can be removed with a toothpick or tweezers. Soft scale insects tend to be more difficult to notice, especially those species which take on the color and appearance of the stem or trunk. Many soft scales, however, have light and dark brown markings that make them fairly easy to detect.