When choosing fonts for web typography, it's easy for a designer to impulsively reach for Open Sans or Lato or Avenir or whatever the newest, hottest thing out there at the time is. I've done it. We all have. There's a compulsion for the fonts we use on the web to match the fonts we use in marketing material, particuarily print. After all - we do want to be on brand, right? But is that the most important thing typography should address?
But if you start to consider your performance budget, using webfonts starts to make less and less sense. Users hate slow websites
Let's pay attention to the words we don't often even bother to look up in the dictionary. Take user interfaces for example:
ˈin(t)ərˌfās - noun
1. a point where two systems, subjects, organizations, etc., meet and interact.
2. a device or program enabling a user to communicate with a computer.
– From Google
Sometimes that problem is for the user, like increasing legibility or reducing cognitive load. Sometimes the problem is for the business, like increasing maintainability and scalability. So maybe that means adding constraints to the design requirements and increasing the efficiency of the system.
But what it does do is this: make your page heavier and harder to maintain. Good web typography should be functional and performant. Everything beyond that is nice to have and should be considered an optimization on an already validated design.
They also allow your site to feel native to the platform in which a user is experiencing it. W3C is already considering this as a standard anyway