The only benefit to online checkin that has been acknowledged by Disney is that it will save you time at the resort check in since they will already have your credit card information.
DVC does not "change" your room assignment just because you don't like it. Any request for a particular location is a request and never guaranteed. Locations are sometimes booking categories such as Boardwalk view, Hospitality House etc and in those cases you will be placed in those categories of villas.
Sometimes you may be able to switch if they have another villa available, however, if you have already gone up to your room you will be charged a fee to do so.