Double breasted jackets tend to have a more formal look to them than the usual single-breasted models. That is why they are ideal when the occasion calls for a more dressy style of attire. As with any other jacket, you should make sure the sleeves are just the right size, as well as the shoulders. It is all too common to see men wearing jackets that are just too big on them.
Two examples – I like the tapered look of the one on the right:
Black double-breasted blazers for men pictured:
Left: Leonardo Valenti Mens Black Blazer Double Breasted Classic Fit Made in Italy Metal Button
Right: Doublju Mens double Gold button tailored Jacket