Import URL in CSS useless?

There's three reasons you don't want to do it in your HTML file.

First, if you use the include directive, you added an extra GET request to your html. The hit isn't that bad on a desktop, but for slower mobile connections, it can be a problem.

Second, will be non-cachable. External links can be cached making subsequent page visits that use the same assets faster. CSS directly embedded will not be cached and your HTML file size will be larger for each page.

Third, your css being embedded means it will both overwrite your external css in priority. If you are mixing both embedded and external CSS , not knowing the priority order will make it a problem when you change a CSS rule in an external sheet and don't see the change get reflected. You'll have to use the hacky !important css rule.

There is a time to use @import though if you switch to using a CSS preprocessor like Sass. Sass will let you keep your stylesheets separate, (which is important if you have to work on a large website), and then combine them into one file when they are needed for processing. It cuts down on requests and makes the code more maintainable.