Fonts and loading time is a big factor in search engine optimization because, when picking a font, its important to consider which character sets are supported. If you need to localize your page content to multiple languages, you should use a font that can deiver a consistent look and experience to your users. For example, Google's noto family aims to support all the world's languages.
The problem with using customs fonts, however, is they can really slow down your site load. Font files are large, can require separate font files for bold and italic, and can block rendering if the developer doesn't work around them. The style and thickness of a font can affect your font's weight. For example, Fredericka the Great and Raleway are considered "heavy fonts". This does not mean that you should never use heavier, styled fonts. You may use heavier fonts in your site title and subtitles.
You should use a simpler font when writing a long paragraph of text. You should refrain from using more than 2-3 font types on your site, this not only helps with your site's loading time, but gives your site a polished, well organized look. As well as Loading time is also a big factor in SEO. Site loading time has increased by an average of 21%. Why? Actually In the past web pages were much simpler. They contained mostly text and lower quality images.which were not that much havier and they took hardly 1-2 seconds to open. These days, there are an ever increasing number of new features available for the web such as: `High quality images `Animations `External applications `Videos `Slideshows and much more
While these features definitely improve a visitor's experience, they do make a site heavier and can result in a slightly increased loading time.