Long radius elbows give less frictional resistance to the fluid than the short elbows.
Long radius elbows create lesser pressure drop than short radius elbows.
Short radius is less costly than long radius elbows.
The short radius elbows are used where there is scarcity of space.
A short radius elbow will be giving the piping a sharper turn than a long radius elbow.
In a long radius elbow the radius of curvature is 1.5 times the nominal diameter. In a standard elbow the radius of curvature is 1.0 times the nominal diameter of the pipe.
In addition to this classification the elbows of 45 degrees, 90 degrees and 180 degrees are called as a return elbow.