I almost never bring wheeled luggage into the plane cabin. Even those smaller ones can be a pain to roll down the narrow plane aisle, maneuver in a crowd of people, handle urban sidewalks etc. If I were doing mostly point A to B travel, like to visit family or go a business trip I generally bring some small "book" bag (maybe 20 liters) and check a wheeled luggage or two. When traveling for a pleasure vacation I usually bring a single travel backpack. 30 liters is best to ease movements between plane, customs, auto, train, bus, motorbike, boat, stairs, walking; but something closer to 45 liters is sometimes needed to fit enough stuff.
I found that needing to bring an extra pair of shoes is one of the biggest obstacles to making a ~30 liter bag work, but when doing one-bag travel I am usually traveling to someplace warm and only need to pack something like a pair of Tevas or Hey-Dudes. Some hand washing in the hotel sink along with laundry service can really reduce the number of items to bring. Carrying a single backpack is liberating when on the move for sightseeing as compared to pulling a bigger suitcase which eventually turns into a load of dirty clothes anyway. But doing laundry on the move does take planning; may need to be staying more than one night in the same place if sending it to some outside service (24 hour turn around), and when hand washing in the room need fabrics that will dry in time to pack in the morning.
I found that needing to bring an extra pair of shoes is one of the biggest obstacles to making a ~30 liter bag work, but when doing one-bag travel I am usually traveling to someplace warm and only need to pack something like a pair of Tevas or Hey-Dudes. Some hand washing in the hotel sink along with laundry service can really reduce the number of items to bring. Carrying a single backpack is liberating when on the move for sightseeing as compared to pulling a bigger suitcase which eventually turns into a load of dirty clothes anyway. But doing laundry on the move does take planning; may need to be staying more than one night in the same place if sending it to some outside service (24 hour turn around), and when hand washing in the room need fabrics that will dry in time to pack in the morning.