A sport coat, blazer, or suit jacket represents a giant leap towards maturity when it comes to dressing well as a man. A properly tailored jacket contributes to a man's pragmatism and ensures that his person is usefully organized, as well as stylish, at all times.
Blazers and suit jackets have been worn by men for the greater part of the past century, and thus wearing one today is a nod towards tradition. Attention should be paid to having multiple blazers that differ in cloth and weight depending on the season and weather they are to be worn in.
In addition to being historic, blazers are also utilitarian in design, and notably pragmatic. Just as a woman has a purse to carry her essentials, a man has a blazer to keep his, often comparably fewer, essential items. A wallet, cell phone, sunglasses, and keys are fair game to be kept in a blazer's pockets. To avoid an 'overstuffed' look, the man should keep these items distributed evenly among all the blazer's pockets, both interior and exterior. This ensures that the overall fit of the jacket won't be affected by pocket 'bulges' happening anywhere. Moreover, one will be more thoroughly organized, as each essential item will have its assigned pocket.