Above are 3 different types of megamenus: a simple 2-D list, a 2-D list with images, and a megamenu with links, descriptions, and video. As you can see from those images, megamenus can be used in a plethora of ways.
The more categories, or pages on the site, the more it is recommended to use megamenus. One good example of this are ecommerce stores who provide a wide variety of products. For example, www.lightexports.com, uses megamenus for each of the dropdowns in the top navigation. From the image below, you can imagine how long a regular 1-Dimensional list (list straight down) would be.
Some websites have a fixed header so users do not have to scroll back to the top in order to use the top navigation. However, having a fixed header means that part of top the browser will always be taken up, and if you have too many options in the dropdown, some options will not be seen. Below you can see an example of this.
In the image above, we are scrolled almost to the bottom of the screen but there are brands that are cut off. Using a simple megamenu has the benefit of allowing more brands to be seen, as shown in the image below.
More brands are visible, and it is a fraction of the height of the simple list. This is another example of how megamenus can be utilized.
Whether you have many pages to show, a lot of information or media you want available, or simply want to add customization to your site, megamenus are an extremely helpful and useful tool to help users navigate the site easier.
