Question

I can see that all big sites store the images on a complete different server. What are the benefits of this practice?

Answer 1

1. Load balancing.
2. Separation of dynamic and static content.
3. Static content is served from servers which are geographically (or in network “length”) close to the client.
4. (Update) forgot to mention that browsers used to limit the number of concurrent requests to the same server or domain (don’t know if it’s still used) and using different domain names allowed the server to bypass this limitation.

This way each kind of server serves resources it’s tuned up for so clients get pages faster.