Garnish is sometimes overlooked in cocktails but I feel it is very important to the overall cocktail experience.
The five senses are: sight, smell, taste, feel, and sound.
Cocktails extenuate the senses. The taste is obvious. Two of the five senses are influenced by the garnish.
The garnish has a lot to do with the wonderfully presented cocktail in front of the guest. A spiral, a horse head, etc... really make for a special presentation.
Not only that, but the garnish provides a very large part of the smell of the cocktail. As the guest takes a sip of the cocktail their nose is pushed in and is consumed by the smell of the garnish itself. Because smell and taste are so closely related the garnish of the drink is extremely important.
Many people take their garnish, squeeze it and drop it into the drink right away. This is a fine practice, but taste the drink before doing so. Take your sip near the garnish so you can get the full aroma. You might be surprised how much better the drink tastes than if you would have put it in the drink.
In some cocktails you could actually consider the garnish an ingredient in the drink. Some drinks require the flavorful scent of the garnish to get the full effect of the cocktail. The mint on top of the Mojito is a good example of this.
So, if it takes you a little longer to garnish that drink... remember that the garnish is actually two of the three senses that you are effecting.
Image courtesy of my wife...