oldbogie Post #9 is right on the button
Ill add this: The main purpose in racing applications of the oil groove was so the oil squirted on the pistons could absorber and dissipate forged high compression piston dome heat (keeping pistons cooler), the groove on the rod isn't needed in lower compression street engines. My pink rods in my 12:1 302 have the grooves, I had to add the groove to my new inserts.
Some of the top racing engine builders add remote oil squirters to lubricate and cool piston undersides. Especially on turbo or supercharged engines. If you depend on strictly splash lubrication to pistons, cylinders and rings? that's a decision for the engine builder
or the engine owner to make!