Embarkation at Charleston was very efficient. There's been a lot of publicity locally about some downtown residents wanting to get rid of the cruise ships, however, as a resident of downtown Charleston, I find their complaints have very little merit. Cruise traffic is directed away from the main city streets (East Bay) onto Concord Street. We had a two-hour afternoon window to enter the port, and there was absolutely no congestion in the middle of that window. Upon entering the port, we had to show our boarding passes & passports about 3 times which sounds like a lot, but overall, we were in the terminal within 5-10 minutes. The terminal line moved a little more slowly, but we were on the ship reasonably fast.
I highly recommend exploring more of Charleston before or after a cruise. It's a beautiful city and the downtown area is easy to walk or you can grab a pedicab. Even as a resident, I enjoy the carriage rides. Look for Larry, one of the carriage horses. Actually, just listen for him. He's very talkative. Bulldog Tours has really cool ghost tours and access to the Old City Jail and the Customs House. The tour guides are all excellent as they have to pass an exam that has a higher failure rate than the Bar Exam. There are also so many amazing restaurants and little places to just sit and sip a drink. Check the calendar for festivals such as Spoleto & it's sister Piccolo Spoleto, the Food Festival, and other events that can be held out at one of the plantations. There's always something going on in the city!
On the day we debarked, it apparently had rained heavily early that morning which made debarkation a little painful. I know blaming the weather sounds ridiculous, but this is the LowCountry. It floods. A lot. Especially at high tide. It slowed things down quite a bit, but we were still off the ship only about an hour late.