In 2001, Illustrator 10 was released with a feature called Slicing. For the most part, slicing is a way to "chop up" a large graphic or parts of an overall design into rectangular regions. These regions are then "sewn together" on a web page using HTML tables, where each rectangle -- or slice -- represents a single cell in the overall table. At the time, building HTML content with tables was a common technique.
These days however, the majority of web pages are built with the far more versatile CSS standard. It's also rare that anyone uses Illustrator to assemble full web pages (graphics are usually created in Illustrator and then exported and assembled using CSS in a program like Dreamweaver for example). So the slicing feature in Illustrator today goes unnoticed for the most part.
In truth, those who use Illustrator for interactive design more often create individual art elements such as various-sized banners for ad campaigns, buttons or graphics for web pages, or icons for apps. Even those who design entire web pages in Illustrator usually end up rebuilding them with CSS, and export individual graphics as needed.
So when it comes to using Illustrator for this type of work, a valuable feature would be one that allows a user to easily define multiple areas within a single document that could each be exported in a variety of formats (PNG, JPG, GIF, etc). When the multiple artboards feature first appeared in Illustrator CS4, and when the feature was enhanced in Illustrator CS5, many thought it was a perfect fit for this kind of work.
