We all think that we are masters at doing this as it seems like such a simple thing to just jam a spoon inside a glass and just do some circles and stuff.

However, the purpose behind stirring in mixing and making cocktails is delicate and requires actual attention. Your goal here is to gently combine the ingredients of your drink and dissolve just enough ice to dilute that mix.  The result is a gentle flavor on the alcohol which makes it more enjoyable for the drinker.

Compared to shaking, stirring is actually such a gentle technique and it is done exclusively in specific scenarios such as :

When the ingredients are made of pure spirits or liquors whichever you like to call it. Even though you can still shake them as some guests or customers might prefer it that way, however it is much better to stir them ( examples of such drinks are the Negroni, Manhattan & Martini )

Above is the main technical aspect of stirring cocktails, but you’ll still find yourself stirring when making a drink directly in the same glass without the use of a mixing cup. Mainly drinks that are served in Collins & Low/Highball glasses would be the nominated subjects ( Example : Whiskey Blends, White Russian etc. ) You can either leave the drink as it is and let the drinker use a stirrer or a straw or you can stir it for them.