OK, my 2 cents on this subject. I am not 100% sure (maybe someone else can pitch in on this), but I would imagine that there are XX number of slots set aside for OCS applications through the Fleet. Maybe not "hard filled" or restricted to enlisted fills only, but the normal year round historical accessions that BUPERs is counting on to fill the ranks from prior enlisted. That would of course be the first advantage that a prior might have over someone straight out of college.
Others I can think of that look good, are the quality of the tour in the Navy that that prior had, did they get warfare qualified, medals and personal awards recieved, etc.
The prior has better access to getting personal letters of recommendations from Officers and NCOs that they WORKED for, and had the opportunity to see them in a real work setting.
The prior has already been evaluated under the Navy's eval system, a form readily understood by the board. Don't know how helpful this would be, since the evals have once again gone back to the old overrated style...
And I think the strongest factor, and as previously mentioned, is the fact that a prior is a PROVEN commodity in some respects. The prior KNOWS what they are getting into, and the chances of that person succeeding in the Fleet and being retained are that much higher. Plus, the Navy likes to promote from within, and keep all that hard taught experience for itself.
Is a prior a shoe in? No, I don't necessarily think so, you still have the ballistic spread from sub par, to mediocore, to stellar sailors. Is it a check in the box for the OCS package? A big YES. Especially when it comes down to breaking a tie between two applicants, a definite factor that would come in to play.
Someone mentioned "expecting more" out of a pior, and I would have to say that that is true for when they get picked up to become an Officer. From my commissioning day on, without a doubt, I have been held to a higher standard than those other freshly minted junior officers. I have been expected not to make the same mistakes and have been weighted down with more responsibility than my non prior peers. COs and XOs look for and expect more out of their mustangs in their wardroom.