It has been ages since I used Hilton's OLCI. I seem to remember ability to choose a room type as well as some upgrade offers (need to paid $) during process. I was diamond so not sure what features (if any) I was offered that others do not see.
I personally never focus on OLCI. If I remember to utilize it, great. If I was too busy or too lazy to use it, not much difference. I do remember using it if I was coming in very late at night. I personally find the bonus points from Amex for Hilton bookings more useful than OLCI.