The module simply removes any indentation in the page source and with this it minimises the size of the page itself. The browser doesn't care about the spaces anyway.
As example Default Opencart install:
Home page before module page size is: 4.3Kb, after adding the module the page size is 3.7Kb
Product page size is before is 6.3Kb, while with this module the page size is 4.4Kb