The ring finger is recognized as the finger that creates rotation.
To reduce the revolutions (and reduce hook and/or backend),
some highly skilled players use this grip. The grip is a combination finger-tip
 and conventional in that the  middle finger is drilled as a finger-tip
span, with the ring finger drilled conventionally. This reduces the leverage
and power generated, which reduces the rev rate and hook on the lane.
This grip works best for players of a higher skill level. Consistency for 
release,hand position,ball speed,revs and accuracy is a must to successfully
utilize this release.