We checked in on-line last year for AKL. When I made the reservation I had a phenomenal CM who took lots of information on our needs. Our room request were more than met and the manager stopped us in the lobby after the first night to make sure we were satisfied with our room. Plus, check in was very fast.
My understanding is that they assign the acciessble rooms and medical needs a couple days in advance. Online check in would assign a room if one had not already been assigned. Really all you are doing with online check in is giving them your CC info earlier!
People in general here have reported positive outcomes with online check in.