The purpose of adaption is to produce a mesh that is fine enough and adequately represents all important features of the geometry. However, when you have a coarse mesh of a geometry that has curved profiles and sharp corners, the adapted mesh may not recover the curved profiles and corners at the perimeter of the geometry. In such cases, you can use geometry-based adaption to reconstruct the geometry (or to recover the finer details of the geometry), while you are also performing the adaption process.