Some think that leaving a gap between the shelf plate and the side plate gives the 4 oclock hen feather clearance. But with a properly tuned arrow, by the time that feather is at the riser it has flexed. If its going to contact the bow it will often contact the outside of the shelf--- the four oclock hen feather can kick off the outside of the shelf causing issues.. A few causes--- arrow not tuned, shelf is too wide, nocking point too low, fletching profile too high, or possibly the release.
Cock feather in pretty much eliminates the chance of fletching contact, since the two hen feathers are now on the outside. Your arrow flexes to where the cock feather is nowhere near the riser ( unless arrow is really off in spine) and the two hen feathers are out of the equation.
Cock feather in just makes sense.