Rotor grooves and sometimes cross drilling are frequently used on racing brake discs to clean the surface of the pad and allow gases produced to escape.
In doing so the friction characteristics are modified, different groove and & drilling patterns affect the friction characteristics in different ways, some affect overall friction and others the bite or release characteristics and therefore the best solution is not necessarily the same for each application.
AP Racing is constantly developing and refining Rotor face patterns. The most popular face types are shown below:-

CG4, 8, 12 & 24 = Curved grooves,
(backward facing)
Digit specifies number of grooves per face.
New standard pattern.

D = Cross drilled
drilled holes chamfered).
Still preferred with some pad materials but can compromise disc life

GA = J hook design.
Latest design gives improved bite and debris clearance and reduces distortion / vibration, outer grooves do not run out to outside diameter.

N.B. Not all face types are available for every disc.