Designer/Programmer for 20 years System font stacks are a way to produce consistent designs across machines. You use them because you know for certain that a f

Designer/Programmer for 20 years System font stacks are a way to produce consistent designs across machines. You use them because you know for certain that a font is installed on a machine. This comes with some benefits. But the primary benefit would be maintaining a certain level of control of the brand/site. By specifying "sans-serif" you are handing over the control of the font to the user. Now if I were to set my default font hypothetically to wingdings, The whole site becomes instantly unusable. That is an extreme for certain, but the point remains valid if I set it Comic sans because i like the look of it. The New York Times would lose the timeless feel and serious nature they have worked hard to evoke. If I changed it to Consolas I would throw the old and well established rules of typography like leading, kerning, line length and visual weight straight in the bin. Many people may not think about those rules, because those rules are like special effects - when they are good, they are invisible. No one stops mid-page to remark how readable something is. Just like no one questions if an Apple store is an apple store. It just is, everything screams "Apple". But change the Apple stores primary colour from white to slightly grey and everything will feel slightly off. You mentioned Wikipedia uses "sans-serif" only yet wikipedia doesnt focus too much on brand or legibility of their content. They focus a lot on the quality of the content. So thats the high-level take on why forcing a system font is preferable for designers, it provides a fairly predictable experience with some well designed default fonts that are already installed, without having to worry about unusual fonts breaking designs. Thinking too much about it is for big corporate site where there is money to care about such things. Often, a Corporate Identity comes down from Marketing and front end guys have to follow it to the letter. (NB I have not mentioned my thoughts on RTL and international languages purely because I am not qualified to do so. Not an expert, just aware this is a massive problem on its own) Having said all of that.. I personally think there is nothing wrong with "font-family: sans-serif;" and use it often.