What to do regarding the deprecation of Sass
Shopify recently announced they will deprecate Sass, and also started showing a warning on the code editor whenever a Sass file is being edited.
Does this change anything for merchants?
Deprecating Sass is a measure Shopify is taking to improve storefront rendering time, the main benefit of the change is an improvement on how fast the theme editor will react to theme settings' changes.
Shopify uses the example of changing fonts on the theme editor, from the moment you select a new font to the moment you see the new font applied on the theme there is a difference of two seconds between the theme that uses Sass and the theme that doesn't use Sass.
It is important to note, however, that this does not represent a difference in loading speeds when someone is visiting your shop. The Sass file needs to be re-rendered only when changed, and if you are not making any changes to the theme's code or settings there is no need to re-render the file and there is no unnecessary delay for your customers.
What actions should you take?
There are no actions required. Shopify will never break themes that use Sass, and your store will continue to work as now forever. However, you may not be able to use new features that Shopify may introduce in the coming years.
We (theme developers) have been notified of this change in mid-2020 and since August 2020, our themes (with the exception of Focal, that is planned to be redone completely around July 2021) no longer use Sass. This means that if you absolutely want a version free of Sass, you can upgrade your theme by following those instructions.