We started to go carry on after retirement. We travel quite a bit.
Why carry on only? First reason is our physical ability to handle it by ourselves. That could be lifting it up to a luggage rack on a train, into a small rental vehicle, up two flights of stairs in a hotel or B&B, along a narrow ramp to board a ferry, or indeed, as in Thailand, carrying it across two ferries tied together and then climbing down a short ladder to get to on to our ferry.
Apart from that we have had some airline connection delays that we were able to make much better by being able to answer in the negative to that question...do you have any checked bags?
Bottom line....it has made our travel much more enjoyable. It took some time to adapt. It is not for everyone. But with the exception of a car trip from home this is what we take for trips of one week to three months.
Recently came back from South and Central America. Started out in the snow where we live, warm in Santiago, BA, cold around the horn, then plenty warm in Chile, then warm in Costa Rica and Panama. Planes, buses, rental cars, trains. Carry on made it so easy. My spouse was somewhat resitent, now she is the biggest proponent.