After takeoff, passengers are free to move about the cabin without fear of disrupting critical weight distribution. But that doesn't necessarily mean it's OK to take over empty seats without warning.

Switching to an empty seat on a plane is generally permitted only after boarding is complete and with the explicit permission of the flight crew. You should never move before takeoff because passenger distribution is critical for the aircraft's weight and balance calculations, especially on smaller regional jets where a single person moving can shift the center of gravity. Furthermore, seat assignments are part of the official manifest used for security and emergency identification. In 2026, airlines are stricter about seat poaching in "Preferred" or "Extra Legroom" sections; if you try to move to a seat with higher value than what you paid for, the crew will likely ask you to return to your original seat or pay an upgrade fee. The best protocol is to wait until the "Fasten Seatbelt" sign is turned off at cruising altitude and then politely ask a flight attendant if a move is possible. On a full flight, switching is rarely allowed to avoid blocking aisles or disrupting the service flow.