I have not tried this before. But for United airlines, I can print the boarding pass at home, but if I have some bags to be checked in, I still have to go to the counter at the airport, so that they can put the tags on the bags.
Yes, it's very convenient. I can fill in all family members' passport numbers and choose or change seats online. This highly reduce the time spent at the counter (even if you have to drop off checked-in baggage there). They usually have a separate line for customers already checked in online so you don't have to line up with everyone else. If you are concerned about your seats, however, do the online check right the earliest that you are allowed to.
All airlines have separate check in counters for electronic & manual............ except Air Canada! I almost missed my flight because of their stupidity. So shocked when I found out that I have to line-up with technology retarders, even thought I've already check-in and got my broading pass! And then, the Air Canada staff at the gate gave me dirty look because I was late. I told him that there was a line-up in check-in, and he said "No, there's not".