This advice is best taken for server software where allocating memory and copying data would be considered a very expensive part of the pipeline. In the vast ma

This advice is best taken for server software where allocating memory and copying data would be considered a very expensive part of the pipeline. In the vast majority of scenarios, any I/O wait or mild to serious computation that has to be done using this data will vastly outweigh the major advantage of memory-mapped files: not having to allocate and copy. As you might imagine, a caching proxy server is extremely well suited for this, as it's basically just shuttling data directly out of it's store and over the socket.