A service as a software substitute (SaaSS) refers to any online service that performs a function that could instead be performed by software on your own computer. For example, Google Docs is a substitute for a traditional word processor such as LibreOffice Writer.
SaaSS represents a threat to your freedom and privacy in a similar way as proprietary software does. By performing the task online—that is, on someone else’s computer—you are ceding control of your own computing to someone else. Furthermore, you are potentially handing over data to another party (e.g., your documents) that would otherwise remain on your own device.