The Choice of Font Makes a Big Difference to Viewers

Web designers often do not think about the font being used by the text portions of their websites' content because the "default" typefaces provided by various authoring programs suffice for the purposes of the majority of users. Whether they are Times New Roman, Arial, Georgia, MS Sans Serif, or many other widely known typefaces, web designers often find standardized fonts interchangeable and use the commonly used typefaces that personally appeal to them the most. It is also common for web designers to use very few different fonts for their websites because pieces of text content that are in close proximity to each other but use different typefaces can come across to viewers as a stylistic clash that causes the website to look less like a unified whole.
A given operating system always comes complete with a typeface that is referred to as its system font. It is a fairly common tactic for web pages to utilize syntax that instructs the clients' browsers to display the text in whatever font is associated with those clients' operating systems. The first benefit in doing so is that a given client's browser will not have to load an external font file in order to display the text content as intended; this cuts down on load times. The second benefit is that the user will assuredly be accustomed to seeing the font on their computer already, so different clients on different computers will always see a typeface that is familiar to them.
A potential downside to relying on the system fonts used by clients, however, is that the different dimensions of each typeface can result in some portions of the content taking up more screen space on some computers than others. If the web page is aesthetically dependent on its content displaying one complete line of text in a given line, a larger typeface may cause certain lines to wrap around to a new line underneath and potentially unbalance the presentation of the content. Various websites may therefore want to choose a common font that will display the same for all clients. For more information click here https://www.reddit.com/r/web_design/comments/9hoyx5/which_font_youll_use_if_your_only_option_is_to/.