Google has, for some time, made "mobile friendly" a requirement for having a good search engine score. But, beginning April 21st, the presence (or not!) of a mobile friendly site will have a significant impact on search results scoring. There's no news on what "significant" actually yet means, but Google don't use such terms lightly. With more searches being made from mobile devices, and with Google ever-expanding it's hyper-local searches based on your physical location, mobile has to be the most-critical thing on our client's minds. It's up to us to make sure they're very much aware of this and don't see mobile as a "nice to have".
Whilst we've built responsive sites for our clients for a little while, we now need to focus our minds - and our clients - on building for mobile first and then designing outwards for desktop and laptop. Mobile is now the default way to browse the general web and we must rapidly transition into a mobile-first design and build ideology. Fun times!