The primary advantage of an aisle seat is unrestricted mobility and autonomy. As an aisle passenger, you have the freedom to stand up, stretch your legs, access the overhead bin, or use the lavatory at any time without having to ask your neighbors to move or awkwardly climb over them. This is particularly valuable on long-haul flights (8+ hours) where the risk of Deep Vein Thrombosis (DVT) makes frequent movement a health necessity. Furthermore, being on the aisle allows you to "lean out" slightly to catch the flight attendant's attention or see when the meal cart is approaching. It also generally provides a bit more lateral shoulder room, as you can lean into the aisle space (as long as a cart isn't passing). For those who suffer from even mild claustrophobia, the open space of the aisle provides a psychological "escape route" that a window or middle seat simply cannot offer.
One key advantage of an aisle seat is easier and quicker access to move around the cabin without needing to disturb other passengers.
This allows for: Convenient trips to the lavatory without having to climb over seatmates. The ability to stand up and stretch your legs more freely during long flights. Faster disembarkation when leaving the plane. Easier access to your carry-on luggage in the overhead bin.
For passengers who value mobility and autonomy during a flight, the aisle seat is often the preferred choice.