We often advise our clients that vents are chosen as per body type. A double vent would suit those that have a bigger and wider form. While, a single vent would suit those that are tall and slender.
However, in the sartorial scheme of things, a single vent arises from equastrian origin. The blazer below illustrates a jacket worn when riding a horse (hacking jacket), this is when a single vent just makes sense. In most cases, a single vent on a non-horse riding suit may look a tad awkward, but again this is dependent on body type and of course, preference.
Savillian Hacking Jacket – navy blue worsted wool, 3 button, single vent. Details: silver buttons, back belt, ticket pocket, velvet collar, purple outside pick stitching, white inside pick stitching, gold piping, lilac lining.