You are next to the door, so can easily get off.
You are never faced with the dilemma of wondering whether to give your seat up for someone (will oldy take offence at implication that they're infirm, is she pregnant or just fat, etc), yet it is more comfortable than standing.
You are next to a window, giving you a bit of a breeze in the summer (the London underground does not have aircon). Likewise, being next to the door, you get a bit of "fresh" air at each platform. If no one is standing directly in front of the window, you have implicit authority over the degree to which it is opened.
The cushions are about 30% wider than a seat, yet are clearly not wide enough for two people (at least two strangers), thus guaranteeing you extra personal space, and reducing the risk of unwanted physical contact with the proletariate.
You have a clear view of the entire carriage, allowing you to discreetly monitor your fellow passengers.