Line Length is an important point of focus when creating a website to ensure that the user has ability to read content on a site without any difficulties. Today the appropriate line length of a website should be 45 to 80 characters per line, although it can depend on your font size. Line length is crucial in UI and UX because as a web developer or a company with a site, you want the user to not just feel comfortable when reading the content, but to be able to receive the information the web page is providing. If the UI has explicity long lines of content and is a struggle to read, then the user might give up and find another website.
Considering the size of your screen device, the main properties to focus on are font size, line length, and line height. The appropriate characters per line being 45-80 as stated earlier, adjusting your line height from about 1.5 to 1.6 for good spacing in between lines so your words aren't so crammed on the page. Crammed lettering and lack of spacing on your lines can give your user an overwhelming experience so line height is an important rule to follow every time you make a new webpage.