How dominant is the mobile web (versus the desktop web)?
I was all set to write an entry about how the increasing dominance of the 'mobile web' (web usage from mobile devices) concerned me, but then I made the mistake of trying to find some reasonably current and solid facts about how web traffic is split between mobile and desktop and how it's been changing. Now I'm writing a different entry, because when I started looking I couldn't find anything that felt solid enough.
Everyone seems to agree that mobile usage as a whole is quite high (at least in first world countries), but a bunch of sources also claim that a lot of that time is spent in apps, not in browsing the web from mobile devices. Google apparently said in 2015 that more searches came from mobile devices than desktops in a number of countries (including the US and Japan). But the only actual usage numbers I could find seem to still have mobile browsing under half of browsing, and apparently not changing too fast; however, I have no idea how trustworthy those numbers are.
(Most people who put forward numbers seem to be out to sell you something, and who knows how reliable their methodologies are. I do believe Google's claim, but they did carefully hedge it.)
There is certainly a 'mobile first' movement for website design, but again there seems to be an aspect of boosterism to it. Certainly there have been plenty of past web design 'trends' that people advocated quite hard for but that never materialized in practice to the degree that their boosters thought (semantic markup, anyone?). And to the extent that this material is produced by pundits, well, pundits have to have something to hold forth about and that's often a future trend instead of a present reality.
(Some of this is a self-fulfilling prophecy, too. Depending on your perspective and how the website works, a 'mobile first' website might either unleash the pent up demand for well-done content from mobile devices or drive away some amount of the remaining desktop usage.)
Sidebar: 'Important' versus 'dominant'
If the mobile web is approaching half of all your web traffic, it's certainly big enough to be worth catering to and designing for. But if it's only (less than) half of traffic you can't focus on it to the exclusion of desktop design, the way you might if desktop usage was (say) only 20% and decreasing.
(It seems pretty clear that including the mobile web in your design is important these days. If nothing else, Google will rap your knuckles in search results if they don't consider you mobile-friendly (although some sources say that that's only for mobile searches).)