If you write a mobile SAP, you may need a quick way to change context. Gestures are limited. If at one point you need buttons / links to be always available for

If you write a mobile SAP, you may need a quick way to change context. Gestures are limited. If at one point you need buttons / links to be always available for the context switch, then a sticky header or/or footer is a logical solution and is what is used in a native apps anyway. It also has the additional benefits of giving you a place to put something helping to identify said context, such as a label, an icon or some shape/color. On a regular desktop you would not have this problem: you can have a menu far away from the content. You can have tool bars. You have the name of the tab and the URL giving you context, and the page need less context switching because you can just display more instead of requiring to juggle with what the viewport can display. But on the mobile, context switching is very hard to do right, and must be accessible from your thumb.