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Have none of you ever worked for a designer or marketing person who was unwilling to accept that a bit of text might wrap on Windows (Arial), but fit on one line on a Mac (Helvetica)? Until we can get the major operating systems to include some of the most popular open-source fonts, we're stuck with web fonts. If macOS, Windows, Debian, iOS, and Android all came with Roboto, Source Sans, Lato, Merriweather, Raleway,…
I think that designers are always trying to get the latest, coolest fonts. If you make Roboto and friends part of the OS, then you'll get a new wave of cool new fonts that aren't a part of the OS. There's always a push from people to have their website look special, and, dare I say it, pop.
Who am I kidding, what they want is Helvetica and for the website to look exactly like the comps they made in Photoshop. Sometimes they're willing to find the money for the license fee and sometimes they're willing to accept Source Sans as a substitute. I've never once had them say "the difference between Helvetica and Arial isn't worth the 250ms delay caused by using a web font."