Small Internet Service Providers (ISPs) cache in order to reduce their line costs, since a large portion of their operating costs is infrastructural rather than staff-related.

Large organizations are usually not short of bandwidth, but their customers occasionally experience slow response times. There are many reasons for this:

• Origin Server Load

  Raw bandwidth is increasing faster than overall computer performance. Many servers act as a back-end for one site, load-balancing incoming requests. Where this is not done, the result is a slow response. Caches prevent slow response times.

• Quick Abort

  Squid can be configured to continue fetching objects, within certain size limits, even if a user who has initiated a download aborts it midway. Since there is a chance of more than one user requesting the same file, it is useful to have the object’s copy in your cache, even if the first user aborts. Where you have access to plenty of bandwidth, this continuous fetching process ensures that you will have a local copy of the object available, just in case someone else requests it. This can drastically reduce latency at the cost of higher bandwidth usage

• Traffic spikes

  Large sport, television and political events can cause spikes in Internet traffic.
  Plan ahead for sports events, but it is difficult to estimate the load that they will eventually cause. If you are a local ISP, and your local team reaches the finals, you are likely to experience a huge peak in traffic. Companies can also be adversely affected by traffic spikes, with the bulk transfer of large databases or presentations flooding the lines at random intervals. Caching cannot completely solve this problem, but it can reduce its impact.

• Costs

  Since Internet connectivity is so expensive, ISPs and their customers reduce their bandwidth requirements with caches.