Last night I checked in right at T-24 for flight from Hou to MCO without EBCI and got A57 & A59. From my past experience, there are likely many others connecting with this flight and we typically get boarding passes in the A30's, so I'd say that EBCI bumped us back 20-30 places.
People use it for the convenience of not having to give up valuable park time to check in @ T-24. That is certainly the reason I signed up for our return trip.
We bought EB as well and got A20 & A21.