In spite of the modern trend towards larger-screen phones, what makes mobile phones so convenient and portable is their small size. Compared with desktop and even laptop screens, phone screens accommodate a lot less content. As a result, screen size is a serious limitation for mobile devices. The content displayed above the fold on a 30 inch monitor requires 5 screenfuls on a small 4-inch screen. Thus, mobile users must (1) incur a higher interaction cost in order to access the same amount of information; (2) rely on their short-term memory to refer to information that is not visible on the screen. It’s thus not surprising that mobile content is twice as difficult.
Whenever you include a new design element or a new piece of content on the mobile screen, something else gets pushed out (or below the fold). Think hard of the opportunity cost of each new element: what does it mean for the users if you leave out element B in order to include element A? Is element A more important than element B? Content and feature prioritization is key. Although we provide general guidelines in this report, your answer likely depends on the kinds of users and tasks that you have.
It seems to me that feature prioritization is often compromised in responsive design. Part of this is the paradigm shift of actually switching to a small-screen first design approach. So often we end up making desktop features fit into a mobile design, because we think that people like feature parity between desktop and mobile viewports. I think in general that’s true, but that would contend that it’s actually content parity that’s more important. At any rate both are clearly it’s important.