So what are we talking about, exactly? Well, when a web developer is bringing to life her design, she must contend with the fact that some viewers will be accessing the final site on mobile devices, or limited bandwith connections. As a result, while it’s tempting to just slice up your Photoshop document and have big images wherever you need them, it’s not very practical to do so, especially with the competing challenges of designing for Retina displays (which need high-res graphics) and slower, capped mobile broadband (which need anything that’ll reduce loading time).