Window seats are preferred by passengers who want to have a view, or a wall which they can lean against. Passengers in seats adjacent to the aisle have the advantage of being able to leave the seat without having to clamber over the other passengers, and having an aisle they can stretch their legs into. If a seat block has three or more seats, there will also be middle seats which are unpopular because the passenger is sandwiched between two other passengers without advantages of either window or aisle seats.[9] Middle seats are typically booked last.[10]