Difference between First order (Draft Quality) and Second order (High Quality) Elements

First order (draft quality) elements has four nodes (all in corners) which are connected linearly with each other. When a geometry is meshed with first order tetrahedral elements, all edges and faces of the geometry are mapped with the tetrahedral element having linear straight edges which in result curved edges can not be mapped properly. However, the second order (high quality) elements has ten nodes (four corner nodes and six mid side nodes). As the second order elements has mid side nodes, it mapped properly at the curved edges of the geometry and give you better results.