Traditional vinaigrette is a combination of oil and vinegar. The ratio of oil to vinegar is long debated and every chef has a different formula. Three or four parts of oil to one part vinaigrette is most accepted.
To make a successful vinaigrette, the oil and vinegar must be well blended by breaking the oil up into smaller droplets so that it will not separate as easily. The process of combining two substances that don't mix well (like oil and vinegar) is called emulsification. The oil gives the luxurious, rich feel in your mouth and distributes the other ingredients to your taste buds. It also helps the dressing cling to the salad greens.
The difficulty is that in three tablespoons or so of vinaigrette there can be 45 grams of fat. Even though the oils used (olive oil for instance) are healthy, the goal is to cut down on the amount of oil and calories while preserving the flavor and texture of a vinaigrette.
Because oils are essentially fat and fat has a lot of calories, looking for alternatives that are lower in calories is key. In the case of making salad dressings honey can be an alternative if it is used carefully. There are essentially twice as many calories in a tablespoon of oil as there are in a tablespoon of honey.
Carefully using honey (or maple syrup or corn syrup) can create the same mouthfeel as oil but reduce the fat and calories.