Todor Nikolov writes:
Bendy bones are a powerful Blender feature. They allow you to rig bendy limbs and smoothly deforming body parts with relative ease. However, they cannot be exported out of Blender (e.g. to Game Engines, other 3d apps etc.).
So if you need to export a character that is using B-Bones, you'll need to convert them to good-old boring "regular" bones. Even if you don't need to export, you could also use Bendy Bones as controls for regular bones. This way you can avoid creating much more complicated rigging setups like Spline IK etc.
Fortunately, converting B-Bones can be done easily using the Armature constraint (NOT Armature modifier ;))
Details in the video: