Our LibGuides already have a horizontal navigation. at the top of the site. Web services want this navigation if we don't use the mega menus. Side navigation works better with keyboard navigation when using screen readers. Subpages also more discernable with side navigation.
Side navigation is usually easier for our users to understand and navigate without being overwhelmed. Here are links to information about studies exploring usability, eye tracking, and other studies indicating that students generally have an easier time seeing and using side navigation:
Responsive Design
LibGuides are made with responsive design. This makes it easier for users on phones, tablets, and other mobile devices to read and use them. However, this means that we need to pay attention to where we place content in guides as it will be rearranged to suit the screen size of the user.