I'm of the opinion that a man should remain dressed during the day, and that means keeping his jacket on at all times. Not only does the line of the jacket cover what may be a less than perfect waistline, but a coat also serves as the professional man's equivalent of a utility belt, providing storage for accessories that would otherwise have no proper place to roost. For being well dressed precludes those nasty plastic belt holders for cell phones and similar electronics.
Now when I make this argument the first thing I hear is that so and so's office is too warm for a jacket. To which I say, wear lighter suits. Personally, I prefer to wear heavier cloth without an overcoat until the temperature falls below freezing but there's nothing wrong with the combination of a topcoat and a lighter suit. Trousers of 11 ounce wool will (barely) suffice for anything short of a February day in Moscow when they are partnered with a below the knee overcoat, and that weight is still comfortable in an over-heated work space. During warmer months, ten ounce cloth is perfectly comfortable in air conditioned rooms.
Like the young man in the Esquire illustration, there's no good reason not to remain dressed during the work day.