Sectional menu is a different menu for every section of a website. For example, BBC website has several sections, such as: Sport, News etc. Every of these sections has its own menu which is visible only when you are at this section.
1. This menu can include a lot of sub-categories.
2. It is usually available on all pages of a section.
3. It simplifies navigation within one section.
1. It is impossible to get from a sub-category of one section to a sub-category of another one. i.e., From "Tennis" in section "Sport" you can't get directly to "Genetics" in a section "Science".
2. People can mix up a main menu and a menu of a section. If you're going to use this menu type, make sure that the main nenu and sectional menus look differently and don't use the same design elements.
To sum up, sectional menu is suitable when you have a lot of sub-categories in one category and you consider that users will probably stay within one category on your site.
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