Translating from wikipedia, instead of contacting the search engine directly, your web ranking software will send the search engine request to the proxy server. The proxy server then forwards the search request on to the search engine, waiting for results. When results are returned, the proxy server then sends those results back to your web ranking software. The caveat is, only one search at a time can be forwarded to a proxy server. By having multiple proxy servers available, you can send more than one search at a time to the search engine. It's even possible to send search requests in parallel to more than one search engine at a time, or have your searches appear as if they are coming from different web browsers too. This parallel process of sending multiple search requests at the same time before waiting on the results to be returned from the search engine is what speeds up the report creation process. Bottom line is, the more ThetaJoin proxy servers your web reporting software is configured to use, the faster your reports can be created.