websites created for a desktop browser usually fall apart when they are opened using devices with smaller screen size, and mobile website browsers support limited design format only, so it's vital to optimise your website for it to function appropriately on all screen resolutions.
if a website designed for a desktop is opened on any other device it requires a lot of zooming in, scrolling and thus it is difficult to navigate, if you want to deliver the best user experience to your online visitors then you have to optimise your website for different screen resolutions.
Even GOOGLE'S algorithm update, "Hummingbird" indicates that google acknowledges the exponential growth of mobile market and is quickly embracing it.
With new devices of diverse screen resolution coming in regularly it is vital to optimise your website design so that it adapts itself to different screen sizes and looks good on a smartphone and tablet too, not just a desktop.
"Mcommerce belongs to the future and early starters will definitely have an advantage over later beginners".