User needs to navigate among a website's main sections while still being able to quickly browse to the subsection of another.
Accordion menus are often used as a website’s main navigation. In this way, it acts much like Navigation Tabs, as menu items are collapsed when a new panel is clicked. Where the Navigation Tabs are most often used horizontally, Accordion menus are most often used vertically.
Accordion menus can however also function quite well as sub-navigation for a specific section of a website.
when browsing onoe piece, and then the user wants to go to another, she needs to browse the other section titles on both endings of the accordion (above and under for vertical, and to the left and to the right for the horizontal)
this problem makes the accordion not suitable for case when the user needs to browse the menu frequently.