The only thing that I found different about online check-in is that I was able online to put in my credit card info. for charging instead of handing the CM my credit card at CL check-in. That is the only thing I recall that was different.
But, it actually worked out well that I did online check-in for BWI/CL because when we arrived we were greeted out front, however, the CM did not escort us upstairs. She had the bellman take us right to our room and there was a "fill-in concierge" at the Innkeeper's Club desk outside the door and he had a packet waiting for us and just handed it to us. So in this case, check-in was probably faster because I had already put in my credit card info. online and we got our packet much faster since it was prepared ahead of time and the desk upstairs was busy with another guest, but we didn't have to wait around for him.
FWIW, our first CL stay was at the YC and we were coming from AKL. I had envisioned being greeted outside (I had given them our exact arrival time since we were coming from AKL), but no one greeted us outside and the bellman told us to go in to check-in. We went inside and must have looked confused because a CM asked if we needed help and I said we were staying CL and he told us to just check-in at the front desk! I knew we were supposed to check-in upstairs, but he told us that it would be quicker to just check-in "over there" and pointed. A few seconds later a CL runner asked who we were and escorted us upstairs. Phew.
The CR can be hit or miss, too. However, every time we've arrived at WL we've been greeted by name by at least one and sometimes two CL runners. They even wait and chat with us while DH parks the car and then they escort us upstairs when DH returns. It's so welcoming and such a great way to start your stay.