Many a times the HTML and associated styles may be developed by a different team and won't contain the extra divs AEM adds - and that messes up the HTML designs when you finally use them within AEM. That's why it would have been good if there's a way to turn off the decoration tags without affecting the edit-ability of the components.
AEM offers clear and simple logic controlling the decoration tags that wrap included components. Whether and how the decoration tag is rendered is defined by the combination of two factors, which this page will dive into:
The component themselves can configure their decoration tag with a set of properties.
The scripts that include components (HTL, JSP, dispatcher, etc) can define the aspects of the decoration tag with include parameters.