Blocked sites commonly blocked sites include Facebook, Twitter, and YouTube. if they are blocked in your office you can use proxies to access them. Proxies also help you prevent Internet trail.
What is an Internet trail?
If you visit any site it errors your IP and can track your location your ISP and other details about your PC including operating system browser screen resolution in order to prevent Rez eking this details you can use proxies which show that all the requests are coming from the proxy server rather than your local PC IP.
Proxies should not be used on e-commerce sites while making payment as you will be marked fraud as they track your billing location with your IP location.