It has a wide variety of uses, including speeding up a web server by caching repeated requests, caching World Wide Web (WWW), Domain Name System (DNS), and other network lookups for a group of people sharing network resources, and aiding security by filtering traffic.

[10][11] Further work on the program was completed at the University of California, San Diego and funded via two grants from the National Science Foundation.

In October 2023, it was revealed that Squid continued to suffer from 35 security vulnerabilities which had not been fixed for two and a half years after their initial reporting.

Squid has some features that can help anonymize connections, such as disabling or changing specific header fields in a client's HTTP requests.

The result, without any action by the clients, is less traffic to the source server, meaning less CPU and memory usage, and less need for bandwidth.

This does, however, mean that the source server cannot accurately report on its traffic numbers without additional configuration, as all requests would seem to have come from the reverse proxy.

This feature is used extensively by video streaming websites such as YouTube, so that if a user clicks to the middle of the video progress bar, the server can begin to send data from the middle of the file, rather than sending the entire file from the beginning and the user waiting for the preceding data to finish loading.

In order for a partial request to be satisfied at a fast speed from cache, Squid requires a full copy of the same object to already exist in its storage.