Thanks for reaching out to Adobe Community.
SPIN reads an XML file and generates static text files from the content. It does so by utilizing a template language to read the XML and generate required files from content with them. Since we are gathering the S&P user information comprehensively in the XML, this allows generation of many standard files required in a general S&P implementation. From S&P level settings files, to presentation and transport templates. Additionally the config files can be retrieved from various locations and run manually or at index time.
For more on this, you can reach out to your consultant.