It minifies your JS and/or CSS files and combines them so the user’s browser won’t have to download many files. This affects the loading speed because there are fewer HTTP requests that are made. Most of the time the browser requests each file just to find out that it hasn’t changed and it can load it from cache. But in the meantime it waits for the HTTP requests to be processed. By merging the files together it has to make only one or two requests. The CSS minifier compresses your CSS files to the absolute limit by stripping out unnecessary spaces and combining some properties together. The files can be up to 50% smaller after compression. It also has the ability to fix some CSS errors and delete duplicating properties, leaving the last one. The JS minifier can compress your JS files and can reduce the file size by half, not considering the time you save from HTTP requests.