Currently, can't use GC to pay for your room (but can go later to have them reverse charges off CC & on to GC) & can't pick up MB if it wasn't mailed to you already (& is only held 24 hours at front desk) & can't opt in to receive no daily housekeeping for $$, & can't get map of resort or any other pertinent resort questions answered if you skip the desk at check in.
This is my short list of what you'll miss, if these don't effect you, then check in online & head straight to your room.