One of the main use cases for Squid Proxy Cache Server is as a proxy server with caching capabilities for a software development company to secure the traffic, speed up the upload, and reduce the traffic for similar websites like Google or loading some media content.
Another use case I have for Squid Proxy Cache Server was creating a secured solution as proxy traffic for a global international endpoint. It helped to create a solution similar to a VPN, but using Squid Proxy Cache Server which was easy to implement and deploy, and bind it with database authentication. Squid Proxy Cache Server has many different features embedded which could help create a solution for any flow that is needed.