For years, the businesses have been using desktop websites as the primary view and then implementing the mobile version either as a second thought or as a reactive approach when things break on varying screen sizes.
An increasing trend has been to use a mobile first approach i.e. designing a website or portal primarily for mobile screens and letting it scale to larger desktop screens.
This decision also depends to a large extent on the target audience.
We at The Web Plant recently came across a very interesting scenario when a customer reached out to us for a an event collaboration platform to be built for parents where they can search for kids events & playdates and join the ones they are interested in. When we further analyzed the requirements and the current process, we realized that the primary audience of this online system is going to be moms of children aged between 0.5-6 years. Knowing the local demographics and usage trends, we already knew that close to 100% of the moms will access this portal from their phones. There are fairly good reason for this assumption:
It made complete sense to design not only as mobile first but as mobile-only portal. So we came up with a design that was exclusively for mobile screens. We tested the prototypes on various mobile screen sizes and adjusted the margins, typography and images+icons primarily for mobiles. If someone happens to access the portal on a larger screen like a laptop, they would see an expanded version of the same user interface. There are several advantages to this approach:
See a working demo of the application below: